The Saph cos got killed in the 80's/90's by insurance companies/car crime etc.I've got an autotrader somewhere with e/f plate saphs for £3500-4000 and that was in 1997!!!!escos were still 12/13k at the cheapest then and IMHO have always been a special car,unlike the Saph,which Incidently I own a Saph so that's an unbiased view.
As said,for £3-4 k now generally your Saph will be a crock of shit,yes there's still bargains but don't forget a standard Saph will always bring in £4k broken as long as it's running ok and an escos more like £7-8k broken so I can't see the prices dropping much more really.
Possibly the small turbo in an undesireable colour on say a cat d or c could dip below £8k but I'd say even the worst escos has to be £10k with a ticket.