A/C not working 3 yrs What is highest $$ for total replacement of A/C? on 2002 Buick Rendezvous

A garage no longer in business worked on my air conditioning system and it never worked afterwards. (I paid over $1,000.) I have no clue WHAT is wrong - have been afraid to take it anywhere since. Afraid to be taken advantage of again - but this 90+ weather is really horrific. Car only has 64,000 miles. Thanks for any help!

Asked by for the 2002 Buick Rendezvous
Look at prices around $1000-2000 at most