I have a 2006 2.3l mazda3. The ac compressor seized about 6 months ago, no leaks.

I'm trying to fix it myself and have done the following:

(1) replaced the compressor with a salvage one and
(2) put a new drier in. I then
(3) pulled a vacuum on the system for about 30min at 28Hg, and
(4) made sure there was no leaks with vacuum off for 5min.
(2) While still under vacuum I put R134 in high side until pressure at low side read 14psi (per manual instructions), this only took an ounce or two
(5) then shut high side and added rest of can to low side (so about 12 oz of r134).
(6) static pressure (ac clutch not engaged) is about 100psi, 75F temp outside)
(7) turned car on and hit ac button, clutch engaged immediately and pressure on low side dropped to about 10 psi and then started to climb, roughly 10 seconds after clutch engaging the low side had risen to about 60 psi and was still climbing, at that point I heard some squealing and shut ac off. I looked over at high side and noticed it was lower than low side reading (but this was when the clutch was now off, didn't see value when clutch was engaged). If I let the system sit a few minutes the pressure equalizes across the two as you would expect.
(8) I took it to a local shop and they said the system looked clean and that it was my compressor.

So I just wanted to run this by others and get some opinions, thoughts, etc. The shop wants 600 for parts (compressor and drier) plus about another 600 for labor and charging. I've called around and pretty much everybody is at 1000+. So at this point I'm looking at buying a new compressor from Autozone, along with another new drier and giving it another shot myself, seeing as how Autozone will probably take it back if i bomb the job.

The only thing I think I could have messed up was the oil in the compressor the manual says about 5.5oz and I put 5 oz in the salvage motor, but I only drained about 2oz out of the seized motor (the same came out of the salvage compressor). Would too much oil cause the high low side pressure I'm having? The shop said it wouldn't.

Thanks for any suggestions!