Man, what zip code were you using to pull up that price?
You've discovered the catch-22 of 4L60E repair. As you reduce cost, you increase risk. It's an inevitability. So you could be out the door for $570 (though you had BETTER put in a hardened sunshell for a few extra $$), but you have to install it yourself and there's no guarrantee how long it will last. Understand that most shops can not absolutely, positively guarrantee it won't fail; they just pad their rates to absorb the inevitable failures so if it's YOUR transmission that fails, you don't pay extra.
How much risk are you willing to take? It's not a "bad" question - it's just reality. How much are you willing to spend to lower your risk? You need to find a point you're comfortable with.
