I remember the twin towers at the old Wembley Stadium being sold for £1. The problem was the buyer was required to arrange (and pay for) removal, transport and storage.
The buyer never collected them.
Removal and storage of a 4 car EMU is likely to be pricier than buying the damn thing to start off with. If you have to factor asbestos removal into the cost (check this hasn't already been done, as I'm pretty sure all contaminated vehicles were dealt with or withdrawn under BR in the late 1980's/early 1990's), this is only going to push the price up even further.
Good luck, but I wonder if you'll be able to successfully preserve more than just one or two vehicles. As far as I'm aware, only the former Ilford Cl306 "Shenfield" unit is the only complete overhead EMU in preservation (and that's in covered storage at Kineton). Otherwise it's just one or two vehicles here and there, like the Cl308 driving trailer at Walthamstow.
O L Leigh