Speaking from very personal opinions I would do the conversion myself. I paid one company (no names as you all know) £4200 to do my car and looking back I would do the conversion myself and probably have a lot better engine than I do now.
You get what you pay for with these conversions. Give Voodoo a call on 07751 232531 and speak about the conversion with Elie. Tell him I sent you and he'll look after you. What they usually do is give you a shopping list and off you go. when you've got everything on the list they'll put it all into your car. Their work is A+ all the time. Just look at Simon Sweetland's mk2 to see what I mean!
If you do the lot yourself you're probably looking at about £1300 for the complete engine and management loom give or take. If you get the ECU, key and clocks you can use the OE management setup. If you want to go standalone such as DTA you'll need a DTA ecu which are £900 new, a loom which are £305+vat from stealth and a map sensor which are about £80. then all that remapped which is about £450 ish ontop. It's a costly path to take, but you get rid of the plagued MAF sensor

Where did you see the quote of £5000 dude?