PSI is not what makes a compressor expensive , it is the CFM [ cubic feet per. min. ] that make a compressor expensive .
Look for that spec. from Metcal to find the minmum CFM , But I would recommend larger than what is required for the [ desoldering gun ] because if you'er setting up a bench , you would find so many other uses for its use that something around 4-8 CFM would cover lots of other tools .
Then the issue is if you buy chineeze junk , you end up replacing frequently , and shortly exceeding the cost of quality .
" Bitch one the 1st time when you buy quality , rather than every time your use junk "
I have found lots of used gear free to cheap and repair for less than half the value .