Very few valves will do any better with your poor water quality. I wouldn't bad mouth the Toro's in this case. It sounds like you've had them apart quite a few times. If it's a Flo-Pro, I could understand, but most of toro's valves last a long time given fair water conditions.
Sand and grit is by far the worst enemy of every component of a sprinkler system. You have to eliminate it! I've built many an oversized filtration system because of this. I've got a residential system that uses three 2" Vu Flow filters for a 30 sprinkler system. Overkill, but necessary.
Filter
You could try
these or
these or
these. None of these fit your price range.
The Toro and Rainbird only prevent clogging of the selonoid. You would still have issues with weeping valves. I'm not familiar with Irritrol valve, so I can't comment on it's filtering capabilities, though I would be skeptical of it's self-flushing capabilities.
Even if you find a valve that works with your bad water, you'll just pass the sand down into your heads. You have to filter it!
This post has been edited 3 times, last edit by "Central Irrigation" (Mar 22nd 2012, 3:34pm)