I did a quick search for a silver 1980 Holdsworth Professional and found the following bike. It doesn't sound like yours, but is illustrative. This type of bike would likely be listed for around $1500 on my local San Francisco Bay area Craigslist. Selling price may be closer to $1000 though. If it were mine, I'd make adjustments to the gearing and stem/seat to make it more comfortable, and continue to enjoy it. Good luck with the sale.
Early 1980's Holdsworth on "bikeville.blogspot.com"
