I bought a 720 (from the eighties) and it's brilliant! I'm favoring it over my Brother Deluxe Zig Zag and my Copper Kenmore. Both machines go for $100 plus used on Ebay and parts are coveted too. So It's definitely a great deal for the price your stating.
I lucked out with mine paying only $25.
Mine is mostly metal, aluminium with a plastic cam stack and that thing that you remove to make it a free arm thingy. Plus two of the side panels so roughly 75-80% metal with a bit of plastic.
I did a google search and found this link. If you're talking about the machine from the 60's Totally buy it, it's definitely worth it.
http://www.retrotechgeneva.net/2012/...na-record.html
I'd say go for it!!!