22LR is always cheap (100 rounds for $8), I stay away from the lead stuff in favor of the FMJ. The lead makes the inside of the barrel harder to clean. As for 12 ga. you can usually find #7 or #8 pretty cheap (25 shells for $8). For target shooting you don't really need anything bigger that #7 or #8.
You can check out http://www.cheaperthandirt.com/ they have 500 rd blazer 1250 fps for $20 and they also have a wide assortment of 12 ga rds including less then lethal. Might be worth checking www.auctionarms.com it's like ebay for guns and they have some good deals on ammo.
Damn you guys are paying alot for ammo. Here in iowa you can get .22lr for about 12-13 dollars for a 550 box of federals and A brick of 100 12ga. in 7-8 shot for 20.95 And that is not on sale