I can get an HP 5412 chassis with eight 24-port GigE PoE modules (192 ports) direct from HP for $22,673.52. That's just barely over £60 a port, and it leaves you four slots in the chassis for expansion.

Or the 4208 with 96 100bT and 96 GigE (no PoE) for $17,479.19 (about £50 a port). No in-chassis expandability, though.

On the other hand, you could go with stackables and get two 2510G-48 48-port GigE switches and four 2610-24 24-port 100bT switches for $6,035.96 (£35 a port). Again, no PoE. Plus you have to contend with probably trunked GigE ports for interconnects, which is certainly not as effective as a backplane. Cheaper, though.

I quote HP numbers because they have prices easily available online. But that should give you ballpark information.