yes, the difficult decisions are upon us. most consumers and unfortunately many techs are uninformed regarding epa mandates and proper procedures to transition. if you are not ready to upgrade your evaporator and possibly some ductwork and you have a working r22 condensing unit of the same tonnage, i would say that is your best option. as 4ft said, no one will offer any kind of warranty. hopefully you will find someone who takes pride in his workmanship. here's the checklist - make sure a new liquid line filter and a suction cleanup filter is installed. pay the contractor to return within 24 - 48 hours later and verify that there is no more than a 2 psi pressure difference across the suction filter (the one installed in the larger line). this is a cleanup filter designed to collect and hold residual acid contamination from the burnout. if it gets restricted, it must be cut out and pipe spliced in its place. discuss this additional trip as part of the service and discuss charges for suction filter removal if it needs to be done. if there is no restriction across it, it can remain. make sure the system is evacuated properly using a vacuum gauge capable of measuring microns. have the evaporator inspected and cleaned if needed. when a compressor burns out, there is usually a reason and in many cases, poor heat transfer at the evaporator is the culprit. you may also want to have the evaporator leak checked with an electronic leak detector before work begins. if a technician has a problem discussing these items, you may not want to use him. after he's gone, it's your baby.
additional safeguards to protect your r22 compressor can be implemented. get a price on installation of low pressure and high pressure cutout switches and a time delay relay. a hard start kit might be a good idea as well. you are right. you will be spending thousands when it comes time to upgrade. protect your r22 compressor by these means and buy as much time as possible. then when you do, educate yourself on every point before spending that kind of money. there are contractors who are not doing it right. good luck.
one more note. some distributors are selling units with r22 compressors, but without the freon. they come charged with a nitrogen holding charge. the epa mandated no more units could be manufactured after dec 31, 2009 containing r22. this loophole buys some time for those who still want a cheaper alternative to total upgrade. however, the clock is ticking and that option could go away.