Another alternative is a buspirate, but it is much slower. [2] If you don't plan on doing this often, it's probably the way to go. Cheap and has the ability to do a lot more than just SPI.
But there is definitely not a need to shell out $100+ for a dediprog.
Big warning, though, if you decide to use any of these methods with a chip that is still on-board, you really should use a benchtop power supply. You run the risk of damaging your device otherwise-- I damaged my Beaglebone Black this way. Your device might be able to supply 3.3v to a small chip, but the board probably will draw more than that depending on isolation.
If you don't have one, find a cruddy ATX PC power supply on craigslist, probably in the free section. The orange lines are 3.3v and will work in a pinch.