There are a few that are worth a bit. Most are old and very tired. If the car was built to last it would have held it's money better, but sadly most get used as daily drivers and a lot of them are getting in dire need of restoration.
The engines are good, but the transmission, exhaust, bodywork etc has not aged well.
You can pick a tatty one up for a few grand. A good condition Williams 1 will probably cost you over 4k.
If you can buy one and restore it to it's original state it would definitely fetch more.