$300 actually buys you a lot these days. I think periodically, Dell.com has a 19" FD Trinitron Dell-branded monitor for a touch over $300. I bought my Samsung 900NF a while back for about $325 or so. It's an excellent, professional-grade monitor but hard to find at a low price.
Honestly if you can afford to spend $300ish, then I'd go w/ Trinitron/Diamondtron which is a nice flat screen. If you're on a true budget, then you can probably spend about $250 for a good 19" shadow mask CRT monitor (more curvature). Samsung has a great line of products at affordable prices these days.
Monitor the Hot Deals forum from time to time (or search). A while back, a clearance Compaq AG 19" CRT was something like less than $250, which is a steal.