My mom bought me a pump from one of her friends, which she didn't use that much. It's a nice Medela one and came with all the extra stuff you can get. I know some people are opposed to using a used pump, but I have also heard of people cleaning the inside of the pump with something like rubbing alcohol and getting new lines, membranes, etc. anyone else use a used pump before??
For the medela, assuming it's the PISA, you can take the face plate off and clean/sanitize. It is recommended you get new tubing ($8 on amazon) and sanitize the flanges/adapters. You should get new membranes every few weeks, depending on how often you pump. I would check the medela website before using rubbing alcohol though just in case. It may damage the diaphragm.
Just verify proper sanitizing and cleaning with they manufacturer and I think it's fine. If you're in the US and you have a non-grandfathered insurance plan, then you should get one for free through insurance. Maybe look into that as well if you're concerned.
Re: Used breast pump...