I noticed that there was a groaning noise when I first start up the car. Found that the power steering fluid was very low. So I took it to the mechanic who said that the power steering pump was leaking. He said that from his supplier, that would be a $650 part, so he advised me to find one on my own.

Any advice on where to get a new or refurbished one? (I was advised to avoid used.)

 

You could get a parts car for $650!
FWIW I replaced mine last year with a used ebay one off an 01 I think, for $40. Works great.

Rock auto has the reman ones for around $160 give or take. It's not technically new, but close enough for this application.

 

Might want to double check the diagnosis as a hose would be more likely and cheaper.