Check any of the big tuner shops. A lot of the big ones get motors from customers that bail out on payments, or from dealers because of oil burning problems. Those motors are often in great condition, and cost around $2000, sometimes less. I've never seen any of the tuners post prices on left behind or banged up motors, but I have heard of people buying from tuners like Lingenfelter...may he rest in peace.
I just swapped the fragged LS1 in my 97, (click HERE for the story)
I used a GMPP LS6 crate engine. it was 5400 for the engine with tax. This is just a long block, no intake, TB, or computer. GMPP also has a fully assembled LS1 crate engine for about 6500 that includes everything, evan a non-emissions engine management computer. They say this engine is for hot rodders and such who want an LS1 for their cars.
Also check the following link. Turn Key engines does souped up LS1 crate applications, and they have many HP options, depending on how mch you want to spend. click HERE to see their website.