Sorry if I sounded rude, but I have bought the cheap ones and I went threw them all the time. You might check out your cables and your grounds as mentioned before.
I've never had one go on my Mustang, but I would assume a bad ground could fry one up quickly. Is your block to firewall ground in good shape?
Personally I run 2 grounds from the block to the chassis. One to the frame rail and one to the firewall.
I am almost positive my solenoid is the original off the car. But when I had a 5.0 I would always get the Borg Warner premium line from Pep Boys. I did go through a few on that, but there was an electrical short in the starter.
It sounds like your starter is drawing too much current. Could be a bad starter (internal short), could be a bad starter cable, could be bad connections at the starter or solenoid. Inspect your cable. If it's old and/or too small of a gage, replace it. If you're using one of the old heavy starters, replace it with one of the new light weight starters from a 5.0. I've had cheap AZ solenoids that lasted for years.