If it gives your PC a new lease of life for another 12 months then yeah 85 quid isnt too bad. Thing is though, they're charging you for stuff you could do yourself. For your 85 quid you could get...

SSD £20
8GB RAM £20
Legit copy of Windows 7 £10
Can of compressed air and thermal paste £10

and have £25 quid left to buy a PPV and a cheeky take-a-way

As long as you know one end of a screwdriver from the other and can follow instructions you should be good with sorting that lot out.