You'll also want to take into account Feature Creep ...
Sure the extra little change they want is only going to take 10 minutes ...
10 minutes work .. minute to upload to the site ... another few minutes to write an email to them .. another conversation on the phone about the change ... another little fix to that .. and so on .. suddenly 10 minutes extra work has become an hour.
(Granted its not always like that)
Pauls recommendation of 33-50% extra is something I find myself not doing sometimes and it works out really not worth it in some cases. (me doing the work without the extra 33 - 50% I should say)
Do up a spec of exactly what you're going giving them
Hosting ??? .. how much will it be for them next year ?
Domain name ??? ...
Support during the year ? ... setting up email addresses for them and so on ?
Graphic design ?? (looking at your current site while its functional its not the greatest in terms of design .. sorry to be harsh .. but you are looking at selling a service so it needs to be said)
HTML / CSS coding ?
Custom Coding / scripting ?
Will you be doing anything with SEO ? ... why isn't their site up there at number 1 ? (they'll ask this) .. getting it there isn't a matter of just dumping in the correct title on pages and a few meta tags. Its actually a LOT of work.
Here is a post I made over on boards with some sample figures thrown in for ease it was related to an IT support / Nixer thing so it might apply to you here as well for your other "work" you're doing on the side ..
boards.ie - View Single Post - Fixing computers on the side
Call out rate ...
its going to take you how long to get there ... its going to take you how long to get back ...
you're going to spend how long on the job ...
Do the usual calculations ... how much do you want to earn a year at this (think if it was your full time job)
(for ease say you want to earn 48K a year ... )
52 weeks in the year ... 4 weeks holidays ...
that means 48 weeks left ...
therefore you have to earn 1k a week on the job ...
a working week means 40 hours ...
1000 / 40 = hourly rate of 25 quid ...
Fixing up a printer = .. house call ...
20 minutes to get there ... 20 minutes to get back ... finding out problem with the printer .. downloaded drivers and so on (potentially) .. updating drivers and so on ... and you're looking at 2 hours work ... not to mention ... 1.5 hours parking ...
so your 50 quid rate in this case is quite appropriate ... given these figures .. maybe more
If you're making that amount then you'll have to pay VAT as well on the service you are offering ... take into consideration VAN costs (insurance / depreciation .. 20% first year and so on... fuel ) ... marketing ... lunch expenses (because you aren't at work) ... and so on. Business premises ... you may want an office ... mobile phone costs (can be damn expensive ringing people having those 10 minutes conversations at your expense) / business cards ... ads in the papers ...
Say you want to take a networking course or something ( add on 1 - 2 grand for this)
48k isn't so much anymore
Tools / equipment / (laptop for diagnoses) / multi-meters / replacement parts costs.
Unfortunately the majority of people don't think of all these things
I also realise you're doing this as a Nixer so to speak ... but think long term ...