If he didn't do the gold standard cylinder leak down test you're wasting your time and money + your mechanic shouldn't be guessing like that. Leak down test is the only sure way to verify need for a valve job and a better solution if indeed that's the case- go purchase a used/ or rebuilt cylinder head and skip the valve job. Then all you need is a head gasket. A used head's about $100 or less, gasket = $35. Labor maybe $75-$125/hr but at least you know that's a set price via book time. book time may say 6 hours so do the math and yeah....lot's less than $2500. First thing I'd do is take it elsewhere.