To be honest I think you've gone the wrong way round, amp power has got quite cheap as of late. So with a budget of £300-400 for an amp, why not think about scrapping the Type R and making the overall budget £400-500 (assuming you were going to pay £90-100 for the Type R), then get the
Alpine Type X for £260 and the
JBL GTO-1201.1 to power it for £140.
That way you're getting a far superior sub, and you've now got the ability to produce 1.5kw RMS as apposed to .5kw RMS, far bigger volume capabilities along with better SQ.
You could then use £50-60 to pay
Jam2008 to build a nice big ported box to house the type X and you will have got yourself a very nice set-up there.