I did mine for ~£1300, but that included a new end plate, and having the porting done professionally. I also needed a new bearing. All that added about £500 on to the rebuild.
If all the housings, plates, rotors and bearings are in good condition you could probably DIY it for £700 ish, maybe a bit less.
As for DIY porting, here are my findings when I was researching (I was going to give it a go myself):
Yes it's possible with a dremel and a template, but the actual port face (and that's all a template is good for) is only a small part of the porting job. The shape of the internal chamber of the port is very important, and that only comes with experience from what I can gather. Also, matching the ports is important too. In the end I just paid the extra to have a pro job done (I took the plates and housings to RX Motors).
Best bet would be to pick up some scrap plates/housings from someone like RX Motors and practise on them. I still have my old plate lying in the garage, I keep meaning to attack it with a dremel.