Join Date: Jul 2005
Bikes: 1984 Trek 520; 1990s Peugeot (Canadian-made) rigid mountain bike; 2007 Bike Friday NWT; misc others
Welcome. $1000 and under is certainly manageable even with new stuff. However, fit is not a problem with used bikes. Once you have an idea of the size of frame you need (and you need to know that whether you buy new or used), it's fairly straightforward to tweak the bike to fit you reasonably well. Adjust the seat height, maybe adjust it forward or backward on it's rails, and adjust the height of the bars. Rarely you might need to replace the handelbar stem or tube if you can't get them high enough or they're too far forward, but usually you don't.
The bigger problem with used bikes is they may have worn out parts and as an inexperienced person you might buy a lemon, and if you go that way be sure to get a bike store or very knowledgeable person check it over for you, but even here it usually works out ok, because even if you have to spend $200 on repairs, the used bike is probably still going to be cheaper than new. But buying new is safer for a new rider.
What sort of riding are you thinking of? Are you young, old, fit, out or shape, competitive, casual etc.?