If you do a search here and on google you'll find lots of info. Very likely the machine will need a complete overhaul if it hasn't been done in the last years of its use. This series is prone to some serious issues, though generally a decent machine. I've rebuilt several of them and they all tend to be prone to the never-needs-oiling lubricant turning to wax over the years. Which means plastic gears that are no longer available can be broken and dials frozen. The cam stacks crack and cost $50 each just for the part and there are a couple other costly parts that tend to go. I usually tell people that if they don't know if it works, is the price worth it for parts alone? I would say the price you quoted is worth it for a parts machine, but plan on upwards of $200-$250 of repairs if you want a working machine.
You can get a free manual and much more info if you choose to from the vintage Viking yahoo group.