Fit them yourself James. Then go and get them balanced locally. It's no big deal to do it, the only problem is breaking the bead between the tyre and the rim. A hammer and a decent block of wood should do it. All you need then is a suitable implement to use as a tyre lever and you're away.
OK so in a perfect world you'd replace the valve as well but you can't have everything. 
Surely you need heavy equipment to fit a tyre to a rim? What about the sealant they use too?
I rekon I might just slip someone a few quid 
it aint sealant james its lube !!
very hard to fit tyres on alloys bud better to get them fitted at tyre place mate usaly charge £10 a tyre inc valve and balance !! 
Many, many, many years ago, I mean a long, long, long, long time ago, I used to be a tyre fitter. I only did it to earn some pocket money on weekends.
We never used machinery to fit tyres to alloy wheels as they were too soft and you risked damaging them. We did use a stand alone machine to break the bead but that never touched the wheel rim. The rim was 'thrown' into the tyre and then fitted over with tyre levers, the other side was normally easier than the first side.
As MarkyMark says, they don't use sealant, it's only a lube to help the tyre fit over the rim and we just used to use fairy liquid although I'm sure there will be a
expensive modern alternative.
As I said above, ideally you would need to fit a new valve but these only pull through the rim although a special tool is used for this.
I'd be surprised if you couldn't get an independant to fit them locally but this would obviously have to be factored into the cost of the tyres.
At the end of the day James, a monkey could fit tyres with a couple of days training. Let's face it, I used to do it.
