2004 Kia Spectra

ok, ac was working great. last summer i noticed it began to take longer to cycle. it cycle on for about 5 seconds and cycle off for about 30 seconds, and repeat. basicly, it wasn' cooling the car. later, it stopped cycling completely. i took it to a local mechanic. they did a dye test, recharge, and still didn't work. he said they looked at all the fuses and checked ok. they by-passed it somehow and told me when they run a hot wire from the battery to the compresor, it begans to cylce but the high pressure side goes up very high, more than it should. he told me to take it in later and charged me 85.00 and told me system needed an entire flush that would cost me 1,100.00!
does this sound right? what could be wrong? HELP