Sounds like you are in the USA?..If you can look on Ebay or Craigslist and perhaps buy yourself a Bike Friday Tikit..You could find a large sized one ..it will be a better ride than a Brompton..It will roll more easily than a Brompton using the handle at the back and be cheaper to buy than a new Brompton..Takes standard parts for a road or MTB..
Having said all that..If you buy a Brompton it will be worth a lot of money 5 or 10 years down the line..
If money is tight find a Dahon Speed P8 ..best 20 inch wheel folder on the market..Very comfortable ride with big apple tyres on..but rather difficult to move when folded....( only my thoughts..sure you will get lots more)