Plenty of tires out there (my faves are the Pirelli Sport Demons), but $50 - $70 a tire is less than I've seen for just about all bike tires. The Sport Demons are now going for $85/f, $115/r in classic 250 sizes, at least on
swmototires, and their price is typically one of the lowest around, especially when you consider no sales tax or shipping charges. The list below (disclaimer: found elsewhere on the net, I didn't create it from scratch) includes most of the available tires that are known to fit the 250, perhaps there's one there that would fit what you're looking for...
Performance Tires
Pirelli Sport Demon
Bridgestone BT45
Dunlop GT501
Metzeler Lasertec
Pirelli MT75
Pirelli ST 66
Avon AM63 Viper Stryke
Pirelli Diablo Scooter
Dunlop GT301
Touring Tires
Metzeler ME 880
Avon Roadrider
Kenda K671 Cruiser S/T
Kenda K657 Sport Challenger
Cheap Tires
Dunlop K630
Dunlop K330
Pirelli MT66
Cheng Shin tires
Maxxis tires
GBC Street Shark
Shinko tires
Like you, I hate not having the tires that I want available when I need them, and even popular tires go out-of-stock often enough that I typically stock at least 1 extra set (and usually 2) for each bike we own in the garage, and once I fit a set onto the bike I'll re-order so I'm never stuck without the preferred tire.