This is an easy one to answer yourself if you know where to look... However, the answer will vary depending on when you do the research. The price will increase as time goes by, they aren't making any more Cafe Corners, Green Grocers or Market StreetsBrickLink is going to have better prices than eBay,.. (catalog listing for all the (modulars)Then go to the catalog entry for each one, for example 10182 Cafe CornerBrickLink Reference Catalog - Set 10182-1 and then view the lots for saleBrickLink Search Results (filter by new if you want)Repeat for all the modulars... For those in production, buy direct from LEGO when they have free shipping (such as now, 30 November 2012)I didn't actually do this but I think, right now, (late 2012) if you want new copies of each, you are looking at around 3500-4000 USD, plus or minus. (Quick check, the cheapest new, MISB Cafe Corner is 1300ish, Green Grocer about 500ish and Market Street around 1300 as well... the others are less since they are still in production, yoiu can probably get all 4 for less than a grand...)
So what does this mean? If you see a LEGO set you like, buy it. Don't wait and pay aftermarket prices! (although I love it when you do, some of those modulars for sale on BL are mine. Think of it as enabling my habit)If you're interested in collecting all the modular buildings I would recommend starting by purchasing all the ones that are available in store today. As of today (11/2013) this includesFire Brigade ($150)Grand Emporium ($150)Pet Shop ($150)Town Hall ($200)Palace Cinema ($150)The Fire Brigade just moved to discontinued status, so if you can find one on the shelves I'd recommend purchasing it now. On my last visit to the Lego store the employees said they won't be getting anymore in stock.The hardest part about the collection is obtaining the buildings that are discontinued. Most sets are discontinued 2-3 years after they are released. I was in a similar situation trying to obtain the Green Grocer and Market Street (already owned Cafe Corner). For both of these sets I used Brick Link to purchase each individual part and assemble the buildings.
It's a lot of work, but the Green Grocer set is now my favorite mainly due to the amount of effort I put into creating it. Here's my recommended process for getting a discontinued set:1) Use Brick Store to create a part list for each building. The part list is sourced from Brick Link and is fairly accurate.2) Use Brick Rake (brickrake) to obtain obtain a store list and price list for the parts in the building.3) If possible, use gurobi [1] (The overall fastest and best supported solver available) to solve the optimization problem of finding the least number of stores with the lowest prices for all the parts you need. Without gurobi you'll have to do a greedy approach (more expensive) or brute force (takes forever) method to solve the optimization problem.4) Use the output parts list to order from the sellers on Brick Link. A sellers inventory changes day to day, so it's best to order from all the sellers as soon as you have the list.You may have to make some substitutes to the parts because some of the listed parts are very specific to the set.
Using this method I was able to build the Green Grocer for ~$400 and Market Street for ~$200. The set is a lot of fun to build and each release seems to get slightly more intricate than the last building. [1] Gurobi has a free academic license if you access it from a .edu domainIf you listen carefully, you can hear the sound of parents everywhere rejoicing as they learn that all of the money they have spent on LEGO over the years is finally going to pay off. So, here’s the word on the street — or rather, the word from a recent Daily Telegraph report that is sending parents into a tailspin: Your LEGO sets may be worth a lot of money, especially if you’ve kept them in the set. According to the Telegraph analysis, this popular children’s toy has yielded a better return within the past 15 years than stock market investments, including gold or bank accounts. Since the year 2000, the average LEGO set has increased in value by 12 percent with each passing year, notably higher than the 9.6 percent return for gold within the same time period.
As it goes with any type of investment, the LEGO that yield the biggest return are the specialty sets that are in the highest demand — think Star Wars, the Taj Mahal, or the Volkswagen Beetle. The LEGO set that wins the grand prize for appreciation is the hotel model “Café Corner,” which was sold in 2007. The 2,056-piece set was originally priced at $132 (£89.99) and now goes for $3,072 (£2,096) after being discontinued, with an investment return of 2,230 percent. Suddenly, the crippling pain of stepping on a LEGO in the middle of the night doesn’t seem so bad — as long as you’ve kept your LEGO sets intact. As Maciorowski points out, LEGO investments will only fetch the highest price if they have been kept in their box, in mint condition. And while used LEGO sets may not be worth as much, it’s still possible that they may yield several hundred dollars a box. All sets released after the new millennium are considered the best investment since they contain more complex and specialty parts.
Since the LEGO company constantly refreshes its product lines and retires old models, any type of set (large, small, or minifig) taking up space on a shelf at home could be worth some extra cash if it’s in fairly good condition. The official Brick Picker site can tell you exactly what type of LEGO investment you have on your hands, and you can also do your own research by checking competitive seller sites like eBay. For the full LEGO sets that have not been unwrapped, it’s worth doing the extra legwork since these pristine sets are worth the most money. While there’s always that rare, golden LEGO that goes for top dollar — like the 14-karat gold LEGO brick priced at $14,000 — this is the first time that regular moms and dads may be getting in on the action. In the past decade, high-dollar LEGOs have been reserved for the LEGO elite, like professional LEGO sculptor Eric Harshbarger’s almost “priceless” desk made from 35,000 LEGOs or the LEGO creations made by former lawyer turned world’s leading LEGO artist, Nathan Sawaya, priced upwards of $60,000.