I'll do my best....
I'll point out before I begin, I personally would not deal with Prestwich Models, all parts would come from Bonzi.
Nimrif models - Makara - £125 I think, I stand to be corrected as there are no prices on his site...
Bonzi Sports - Zenoah G260pum with mounts and collets - $279.95 - £170.74 at time of writing
Prestwich Models - Tuned Pipe - £69.50
Stinger assembly with stuff tube and flexi - £47.90
Rudder - £26.95
Prop - various choices specific to engine, lake etc, but all are around £20
Radio box - £24.95
FlexHex - 12.95
Manifold - £25
LMS (local model shop) - Ripmax Fuel tank, one of the big yellow jobs - £8.35
Cost so far - £530.94
You will also need a controller (obviously) for which a Spektum DX5e is excellent, so thats an extra £60
Other accessories such as a couple of bits of Marine Grade ply to make the engine rails, some rx aerial tubes, £5.79 a can for paint and primer from Halfords, some Tygon petrol tubing, an NGK Iridium spark plug, and an Rx battery.
So then, to fit out a Makara would be £ 590.94, plus the extra bits above, and also for radio boxes use a metal sandwich tin with some self adhesive neoprene inside, which are from camping shops for £8. To use Bonzi from america is a lot cheaper than Prestwich, so we shall say for the purposes of this if you spend over £600 you have gone seriously wrong somewhere
Makara - £600 absolute maximum
King Of Shaves - £625, then all of the above to replace the simply awful bits already installed.
It would be far better as a first boat to fit out an AA / A class boat, which will be a considerable amount cheaper than this, but we like the expensive stuff don't we?
Also, as a personal thing, If I had the money to do this and not just the knowhow, I would fit a Bonzi BZX4 engine, 5.5HP@16,800RPM equals one veryveryvery fast boat!
http://bonzisports.com/