Even if your numbers are right it's so much cheaper to use 2 or 4 DSLRs with kit lenses (Canon's EF-S 18-55mm 1:3.5-5.6 IS for example has practically no distortion, so no reason to spend more than $ 175 on a lense). Most projects I've seen in the last year use the 450D, which costs roughly $ 600 including the lense I mentioned above. It features 12.2 MP and IIRC its successor will feature 15 MP for the same price. Canon is very popular in that field because they are the only manufacturer offering a stable API for accessing their cameras.
You can find further information here
. There is also Atiz
which offers very promising sets including software. I haven't seen their products in action yet (they don't do much business in Europe) and AFAIK they only offer book scanning devices, but the software should be able to do maps as well.
Another option is to use traditional overhead scanners. They are extremely expensive but their quality is unmatched. Zeutschel and Imageware are pretty large manufacturers.