types of projector screens?

i see 92" screens (home theater) from $150 all the way to $1000. what should i know about buying these screens ? im on a budget, and seek decent hd images from my 720p projector, not willing to pay 1000 bucks though

There are indeed a wide range of prices for screens. Largely this is related to both construction and performance. Some differences show up in things like stiffness/ridgidity of the frames on fixed screens (impact on flatness of the screen surface), width and effectiveness of masking, ease and smoothness of operation (motorized or portable screens), etc. Performance differences can be more subtle, including things like colour / brightness uniformity (the latter is called hotspoting), sharpness, contrast and viewing angle (usually measured as the angle where brightness drops off by 50%).

To a degree some of these factors are predictable tradeoffs (for example, higher gain screens are known to be (more) prone to hotspoting and narrower viewing angles), but others such as colour variation and build quality issues are not.

As with most things in life you get what you pay for. That said, some screens are better value and not everyone cares or needs the "best". The 1st link is a primer on buying a screen and the 2nd is to a comparitive review of several screens. They provide a good look at many of the issues.

Personally, I use a painted screen I did myself for under $50 following a "recipe" I got from AVS Forum (see 3rd link). I had intended it to be temporary until I could afford a good screen, but it has worked so well I don't know if that will ever happen. See the third link for some screen shots (bottom of the page).