The price on the C4 is a good price. I just had my C6 rebuilt, and built to the max. I went with a manual/automatic valve body, extra clutches, new 1800 rpm torque converter, stage-2 shift kit..... cost me a little over $900 (very reputable tranny builder). And, he's giving me a 24,000 mile gaurantee......even after seeing the engine it was going behind....my built and punched 400. He said he would make it fun for me, and oh my, it is fun. That automatic/manual valve body is sweet. No more kickdown linkages for me. It's like a standard tranny without the clutch.
Back to your 347 stroker, I believe Ford SVO has a crate 347 that puts out 450 HP and 400 ft-lbs torque, but costs around $6500, and I'm not even sure if it is complete..........ie, intake and exhaust (headers).... You will need the money to do one though. Most 347 kits start around $1000-$1500, and that won't include, your machining (block and heads) or any of your valve train components (the kits I've seen anyway).