IAR Systems and AMTEL market the $295 AT91SAM7S KickStart Kit :

Although 300 dollars sounds inexpensive, they are probably making 260 dollars profit after deducting materials expenses.

A better hardware value for less money is a new or used 16Mhz Nintendo GameBoy Advance for testing on actual hardware.

If you have 149 dollars to spare, a Nintendo DS is better hardware value too. Especially because it is fully virtualized in software on OSX (soon).

If you are developing ARM7 thumb USB devices though, that $295 AT91SAM7S KickStart Kit is a joy! They also have Cortex A4 boards.