What if i just got a regular valve from home depot and smeared some JB weld over the threads...
I figure if JB weld can hold up to car engine heat it can handle boiling wort right?
I wouldn't do it. For one thing, do you KNOW if JB weld is food safe at boiling temperatures (the metal will be much hotter on the outside of the kettle)?? Plus, with a threaded fitting, you can take it apart to clean/replace easily. With the JB, it's probably not going to come apart too easily.
I've used brass, one piece, valves before since they were cheaper. But I've since moved to all stainless steel 3-piece valves. You can get those for about $20 each (or less if you hunt around a bit, or wait for specials). Depending on what you're going to put on the inside of the kettle, you could just go with a NPT nipple and lock nut to secure it (plus a couple of silicone washers/o-rings). Put some teflon tape on the threads and you should be leak-free.
Depending on where you go to purchase the hardware, you could get a valve installed for under $30 (all the hardware, plus shipping). That's with just the ball valve, nipple, lock nut, and o-rings and such. If you want to have something else inside the kettle, connected to the ball valve, then that will be extra. I used the above mentioned configuration in my two aluminum kettles with solid results.
Personally, I'd use a hole cutter made to go through metal. A hole saw is rather cheap in the 7/8" size you'll need. Or you could get a step bit that has that size in it's range (usually a bit more expensive though).
I seriously doubt you'll find any/many that used something like JB weld to hold the valve in place.