I sometimes find a decent S10 T5 at my local Pull-a-Part for about $130 plus I have 30 days to return it for any reason.
When I find them on CL it's more of a gamble. Maybe less of a gamble for me since I usually can repair simple stuff. I have extra parts in case you need something. Just ask.
I am always amazed how much people want for a transmission even though they have no idea if it's ready to be put into service. For the T5's with a VSS speedo and being sold "as is", I won't pay more than $100.
