Looking for some advice...

I've searched around the forums and learnt a fair bit from sheldon brown's site so I know some basics

What sort of price range should I expect, having my lack of expertise, in either getting a simple/standard first fixed-gear bike off the peg, or in building or altering one through the help of others, and if so what frame should I be aiming for etc. I like to make my money count, and although I can respect that business has to turn a profit I'm not really willing to go blowing a bundle of cash on a poorly made, dangerous or uncomfortable ride without researching or at least asking for some advice of those who already know better. I'd like to stick as close to/or as less than £300 as possible, at least in starting out.
Si

First there's the OTP option, if you go that route a Fuji Track would be suitable for your price range. A bit dull though, especially if you think you might enjoy the build.

Well, first off do you know how to lace/true a wheel? Or would you be comfortable learning? If you're looking to convert then look for a bike with a decent frame to start with, 531 or similar. What you will then need to do is:

1. Get a fixed hub for the rear (unless you fancy chancing it without a lockring).

2. Lace up that hub and true the rear wheel, you'll prob want to buy new spokes and a new rim too, although if you're on a budget you could use the same rim if it has the right number of holes for the hub.

3. Get some short stack bolts, take off the outer chainrings.

4. Whack a fixed cog on your new rear wheel.

5. Get the chainline right. You have two things to play with - spacers on the front for the chainring and the spacing on the back. Unless someone else does it, you will need a chain tool and cone spanners.

6. Get the tension right. You did get a frame with horizontal dropouts didn't you? Also make sure if buying second-hand that the chainring/spider are connected with proper stack bolts, not rivited as on some cheaper models. You need proper stack bolts to get the tension roughly even all the way around. If you're running ss it's not so much of an issue, for fg it is.

That's the basics, it doesn't have to be a money pit but it depends on how much you are willing or able to do yourself. In terms of cash I would say (with nothing fancy) roughly:

Bike to convert £100 - £150.
Rear hub £30 - £60.
Rear rim, spokes, cog. - £60.

So you are looking at about £250, but if you have no tools or can't do it yourself it will be more. Plus you'll prob want a new chain while you are at it. if you don't own a spoke wrench, cone spanners or chain tool either then we are closer to £300.

Personally I think building up your own is far more rewarding, depends on how confident you are really. If money is really tight then an OTP does at least give an upfront cost. It shouldn't be a money pit and certainly not unsafe if you find a nice bike to start and do it right, just depends on how much time and effort you are willing to spend on it.