Give this some thought. Downtube is active on this forum so you can ask any questions you might have.
Downtube Nova - Lightweight Folding Bicycle

I wouldn't spend a lot if this is your first bike, but enough to get something that rides acceptably. Personally, I would consider it a semi-disposable purchase...buy it, use it, thrash it. Then, if you find you actually do like and will continue to ride, save up for something halfway good. You will have a better idea then what your needs and wants are, anyway.