Hi
@TheJay and welcome.
I don't know this particular model, but I had a very similar machine (a 1978 model) which I sold a couple of years ago for around £50. I was able to let the prospective buyer try out the machine, which had been in use up until the time of sale. Also it had recently been serviced. This all adds to the value as it reassures the buyer. As the cost of service would be higher than the sale price, it's probably not worth it if you simply want to sell, though.
You could look at the prices on Gumtree and or Ebay to get some idea of what to charge, but the truth is that the older machines don't command high prices, even if they are clean and in full working order.
Good luck! Maybe you'll decide to keep it and do some sewing on it?