The back ones are pretty easy - much easier than the front. Obviously you'll need a jack, axle stands and socket wrench - worth checking but I think the top of the strut needs a 16mm socket and the bottom bolt needs an 18mm. You might be able to do it without, but a spring compressor comes in very handy to get the old spring out and put the new one in. The new one will have an adjuster on the bottom which, when you can screw in/out using the provided C-spanner to get it at the desired height - really easy to do yourself. I wound mine to the very bottom before fitting to set it at its lowest. Then jack the car up and turn clockwise with the C-spanner to raise it up if needed.
Any questions let me know. Fitting the Jamex was the first thing I had attempted relating to the suspension and the back ones really were pretty straightforward - just the front ones that are a b!tch to get out.
However a decent spring compressor will cost you £20+, and £80 doesn't sound a bad price to me for having the whole lot fitted. Like I say, if you want to adjust them afterwards all you will need is a jack, axle stands (to be safe) and the C-spanner which comes in the box with the coilovers.
Will