Tom:

My '87 didn't blow cold when I bought it in '01.  In
'05, I decided to get the A/C working.  The shop I took
it to proposed pumping it up with some old freon,
checking for leaks, then making a proposal based on
what they found to convert to 134a.  They had a fixed
price for doing this--about $70, I think.

They found it held pressure and all worked, so they then
evacuated it, put in 134a, and charged me about $150 total.

They did not replace the receiver/dryer or hoses.  It ran
cold for two summers just fine.  This spring I had to have
the seals in the compressor replaced because I let it sit
unstarted for 4 months.

Richard
Boulder