Thanks for this matey, added to my 'list of bike jobs' for the weekend!
It's not hard but coming from not knowing, learning and then getting it right it depends how valuable that £50 is to you. Certainly replacing brake and gear cables along with checking and reindexing the cassette (along with cleaning it) is good for £50. It's beyond me currently.
It took me 3 hours last saturday to remove my chain, chainrings and cassette and clean it all and reassemble. Another hour and a half to clean my frame tuesday and then half an hour to check and refit my headset last night. 5 hours of work for me, probably 2-3 hours at a LBS for £50 is a pretty good rate?
I got a parktools toolkit from planetx for £20 and it had all those tools in along with many others. With cycles the 'difficult' part is making sure you have the right tools and can find instructions how to do things. The actual work is generally straight forward once you have those things. The hard part is knowing if you've done it correctly!
There's no reason you shouldn't be doing it then! I'm an IT guy but always taken things apart to 'figure out how they work', I've done stuff on cars (mostly just brakes, discs and pads) and have done other mechanical stuff before (farm boy born and raised!).
Servicing your own bike is a good feeling and I can afford the time to learn to do it myself, rather than the expense to get someone else to do it!
Saves me even more money for cycling gear!