LS7 goes for 13K in crate form. From there, add an ECU and harness. ECU = good luck not getting raped on GM prices, expect to pay about 1K. The Harness, you can get custom made for anywhere from 500-1000 depending on who you go to and how inclusive you need it. The crate motor doesn't come with accessories, either. That's gonna run you just under $900 after shipping for the entire accessory kit (at least it's all-inclusive). You're also either going to need the gas pedal assembly ($150-250 used) and some fabwork to retrofit, or a throttle body replacement to get you back to cable. $300 there. You're close to 16K now. You can either go old school with a base LS2 or LS1 oil pan and run a wet sump, or run yourself about $1500-$3K piecing together the dry sump system. Now you're likely over 18K. I hope you already have a tranny and adequate cooling system. Seeing as how you asked about putting it into a '95 Camaro, I assume you're swapping out the V6, in which case you can expect to add another $2200+ to get one with a clutch.

As for an LS2, you can find them used pretty easily. Expect to pay $8K+ to get one from a reputable yard with a warranty. This is an all-inclusive deal which will include the tranny, gas pedal, ECU, harness, oil pan (front sump, likely unusable for you). I know of 3 long blocks for sale right now without tranny, harness, or ECU. These are ranging from $2K-$4K, with slightly different inclusions. Again, you'll have to do some piecing together.

Also, going with the LS's T56, you're going to have to custom make a driveshaft. If you are converting from a V6, gonna need a rear end, I assume (I doubt they used the same).

I don't know prices on LT1s, I only know it will be WORLDS cheaper.