I still have one in use I bought for a fiver at a boot market about 5/6 years ago. Going by the labels and corroded casing, it's well old but it still works fine. When I bought it, I had to replace the cables to the carbon brushes as where they come out the casing the red was thread bare and shorting. It took maybe an hour to get it all sorted out.
At the time I was using a 2/3 year old flojet pump that was starting to sound dodgy. I saw the pump in a Sunday market and though for a fiver, it has to worth it as a spare and even if it's naff, I've only lost a fiver. A short time later and with plenty of black acrid smoke, the flojet packed up.
The other pump, about 3 years old.