But if you must use an old flash, then $100 is a lot cheaper than most new cameras. Damage can be cumulative, not just an immediate kill, BTW. Otherwise, consider just NOT using old flashes just because you have one...... I like to try old gear out, sometimes, and I got my Wein Safe Sync for considerably under list price on eBay. By the way, where, exactly, are you finding new flashes for less than 50 pounds???
It's not old flash. The Vivitar 283 is about as old as the Nikon F3. Back then I never heard of high trigger voltage because people assumed that all flashes had high trigger voltage. I would not hesitate to use the 283 on the F3 although to do that the OP must buy an hot shoe adapter unless the OP has the F3P.