IDK what maintenance costs by you, but it's $65 without parts just the basic tune up here. My guy is great about scouring the internet for me to keep the parts cost down but it's not uncommon to pay$100 each visit which I think I'm supposed to do every year. I guess it depends how much sentimental value it holds for you and how you plan to use it.
http://www.tias.com/173/PictPage/1922568974.html
I picked up an old singer at a yard sale for a steal, the online date is 1913, got lucky with all original parts in working condition which cost me $65 to find out.