My 2 cents to welding - weld as much as possible in place. Unless you can tie the tubing down when out of location, especially if you're making multiple welds, the tubing will move. How much it moves depends on the number of welds and the amount of heat applied to each one, as mentioned above.
On mine I just tried to at least get three points of tack and then when I got it all out from underneath the truck I did more attacking and then skip welded from one side to the other..
Again less than $100 for the pipes and less than 50 for the mufflers and about $10 in paint... And $100 for the Harbor Freight welder... I've had friends paid well over $1,000 to have an exhaust system put in their cars...
There's the difference between cheaping out and getting the correct things done had a good cost....
