I'm going to guess it's this one : http://possumjimandelizabeth.com/xht...g_sing360.html
. OLDER Singers have a great reputation, newer ones not so much.
It looks like a decent machine if all the parts are there and in working order. Does it come with cams and attachments, et cetera. I am not familiar with this model, so I don't have ant personal experience with handling (it appears to be a 70s model ?).
The weak point, as noted on that web-site is the fact that it's belt, not gear driven. This might be an area of the machine that needs replacing, and even if it doesn't immediately, you'll want to make sure it can be replaced if it needs to be in the future.
You may NOT be able to bring this machine in to a store where "Singer Techs" or whoever are. They may simply want to sell you a new machine instead of working with your old one and may not know HOW to fix it. You need to find someone who can evaluate the machine before you use it - to make sure there aren't any big problems that could cause the machine to kerflopple on you and become toast.
I'm lucky to have a fellow who repairs older machines locally and does fantastic work.
He even makes new parts for machines and has a large collection of broken machines to salvage parts from.
You will need to oil this machine on a regular basis. This is MUST for many older machines, and newer ones need servicing, too. I think oiling for ever 30-40 hours of work is recommended for older machines. Not sure about a 70s machine, but I'd guess so. You can get the manual for free to check from Singer's web-site.
Is it worth $75 ? I don't know. Try looking on eBay for the model and see what it's going for. Google it and see what others are selling it for. I got my machine for $20 (cost $60 in repairs, so $80 in the end), but I've seen it go for $400.
If this is local, see if you can use the machine before buying. Sew on it with a bit of scrap fabric. Make sure everything runs smoothly - no scary noises, no herky-jerky electrical flow, et cetera.