Try to at least sit on some bikes at your local shops, to get a feel for what size is best for you. The shop guys will want to tell you about their bikes. Listen to them, you might learn something. Ask about their used bikes.

If you want to pay cash and $400 is your preferred limit, then also start looking on your local - or closest - Craigslist for used bikes in your size. Don't be put off by prices which are above your limit. Prices are negotiable. (They're negotiable at the shops, too.) The posted price is just an asking price.

When buying used, you're substituting time for money. Patience and persistence.