doing it yourself is very straightforward when you've done it a few times.
to expand on jt's post, you will also need a cassette lockring removal tool - I think jt is calling this a spline remover - Shimano specific of course but many companies make them. getting used to using a chainwhip is the hardest part but once you know how it works, it's easy (loads of YouTube vids around or go to the Park Tools website for info).
you are also supposed to refit the lockring at the correct torque (around 40nM - should be marked on the lockring) so a torque wrench could be useful as well but again with experience, you tend to get a feel for what 40nM feels like. but you can use a torque wrench for all sorts of tightening so it's a worthwhile tool to have in your armoury (mine came from Lidl for about £12 I think)
and one other thing when putting a chain back on - get a piece of wire (an old coat hanger is good) about 10cm long and bend the ends down so they fit inside a link at either end and use that to hold the chain together while you're rejoining it, otherwise you'll frustrate yourself fighting against the deraileur spring tension! make sure you leave enough links free so you can fiddle about with the rejoining. believe me that bit of wire will be your chain friend for life for zero cost!!!