I doubt its the clutch unless the pressure plate is broken but you'd have lots of noise if that was the case. Its most likely the clutch slave cylinder sprung a leak and you have no more fluid. Running the master dry will also kill the seals in it sometimes.
The slave could be fine and just the master pooched too. Neither of these repairs would be $700. If the clutch pressure plate is fucked and its not a miss diagnosis by the shop $700 is pretty cheap.

Clutch slave cylinder for sure... and yes, it's inside the trans case so it needs to be dropped. Should not have needed a new clutch disc, I would not be paying them shit.

The 98's aren't too bad (Isuzu-designed, but GM-built, transmission), the newer Getrags have more issues with the master and slave crapping out due to shit design.

any updates?

as mentioned many times clutch master or slave had that happen to me 3 times in a few of my previous cars

if ur inspection plate is big enough to see your flywheel/clutch etc. ask them to put the car on the hoist and see your "brand new entire clutch setup" Lol. if its dirty as balls you know they didnt change shit.

Its A good idea to ask for the old clutch / proof of purchase of the new one as well

When the vehicle was dropped off, you would have been asked to sign a repair order/work order before they begin work on it.
1) Did you sign this repair order?
2) What were the instructions on the repair order? (Diagnose only, diagnose and repair, etc.)
3) Did they call and report the findings/the "cause of failure" and give you an estimate for the repairs?
4) Did you authorize the repair?

If you've answered "no" to any of the questions above, you're pretty much in the clear. By signing the repair order, you've enter into a contract to have them perform whatever is stated on the repair order, and you to pay for such services. They cannot spend your money before telling you what your vehicle needs and how much it's going to cost AFTER THEY'VE REPAIRED IT! You are protected as a consumer against BS like this.

Having said that, they are well within their rights to return your vehicle back to the same condition which it was towed in, unless it is unsafe to do so.

PS Always asked them to keep the defective part for you. This USUALLY keeps them honest. Hope this helps.