Long story short: I applied for a (CakePHP, MySQL, etc) development job in London, UK. I grew up in Britain but am currently based quite a few thousand miles away in Canada, so I wasn't really expecting success. But quite a few emails and phone interviews later it seems that they really like me. At least to a point. Because such a major relocation would be a horrible thing to go wrong, they've sensibly suggested a trial run of getting me to build a website at a distance.

I have the spec for this and it's quite a substantial amount of work. My problem is that I now need to suggest both a fee and a timescale for the job, and I haven't got any significant experience of working as a contractor. Looking at the spec, which is 1500 words of many concisely stated features, some fairly trivial and some moderately involved, I can easily imagine there being 2 weeks of intensive work there. (If everything went really well it might be closer to one week, but even though I want to impress, I definitely don't want to fall into the inexperienced-contractor trap of massively underestimating the amount of time a project will run to.)

As an extra complication, there is no expectation that I should give up my day job to get this trial project done, so the hours will have to be clawed from evenings and weekends. I don't want to overcommit to a quick delivery date, only to find myself swiftly burning out due to an unrealistic workload.

So, any advice for me? My main question is, what is a realistic hourly figure to demand of a stable but not excessively wealthy London-based company in the current market, bearing in mind that I'd like them to hire me afterwards? But any more general recommendations based on my circumstances above would be much appreciated too.

Many thanks!