Price vs. Value. How I look at it is that it's good to save money, but if you pay 20% more and are 80% happier then it is money well spent, and that cheaper part would have been a rip-off. Pay a little more, get a lot more, pay a little less, get a lot less.
Welding up some stock
control arms, if you have a welder, why not, spend that money on something else and get faster, cheaper. However, don't hire someone to weld it, because they will still be flimsy compared to some good arms. Actually, most of the
control arms out are rather cheap, until you start stepping up to the more specialized items, then it gets costly.
Don't skimp on rear
suspension because your rear end is key to stability of your car. The rear coming around on you and moving about is the worse part of handling on these cars. Get that rear stable, and not only will it handle better, take off better, but it will be much more predictable. On the mustang, the floating rear axel is really floating. Raise it up and use a prybar and see how much you can move the rear end around. You can even use your hands.