buy the one piece floorboard that comes with the transmission tunnel, rear section, and all the brackets. there is also a front pan section on each side you may need. take out the entire interior before you go up there and it will cost a little less. (bolt the driver's seat back in or have it towed)

i cant hazard a guess at the welding cost, but shop around, and avoid the shop with the cheapest price unless they have an excellent reputation.