Get 5 of these:POWMAX PSDE480 ATX 480W Power Supply
at 5.99 each after rebate they are disposable.
Getting a bit more serious - the only model under $30 from Newegg that I would even think about installing is:FSP Group (Fortron Source) FSP270-50SNV MicroATX 270W Power Supply
This only provides 270Watts, though it is manufactured by one of the best companies out there.
NOW - let's get serious. First you need to figure out what you really need for power. 270Watts is fine for some situations, but definatly not for many others. There are system power estimators out there - put in your specs and figure out what you need.
Second - once you figure out how many watts you really need, add in between 20-50% of head room - as you never want to run equiptment at it's peak.
Third - double or tripple your likely budget. Very few people on Toms' will reccomend any PS for less than $30. Expect to pay at least $70-$150 for something with the proper engineering and components to actually last longer than a year. Choose a brand with some market saturation, cruise through Tom's Forum and find some name brands to research, and try not to buy junk (unless you really want junk.)
Finally - I do not intend any instult here - but before you ask questions like this it is best to describe in more detail what your needs are and what existing or future hardware you plan to support.