A quick scan of Pistonheads reveals only one Mk2 vRS for sale at £7k - the rest are pretty much £8k and above confirming my suspicions (supported by what I still beleive to be an accurate trade valuation) that £7k Mk2's are the bottom of the barrel.
There are only two for under £7k on the whole of Autotrader - one of which has 126k miles on it which I guess isnt the sort of thing you are after.
So, not really seeing that 'a vRS can be had for around £7k'.
I also doubt many dealers will give you spot on trade money in a sale which involves cash your way, either. They'll sense the 'desperation' (ie, the fact you have to trade it) and offers will reflect this.
If you are finding your Focus unaffordable at present then its probably best to go for something that will yield a genuine saving without having to scrape the barrel, perhaps a nice, reasonabely late sub £5k Mk1 will be a better buy?