People pay others to do what some consider a simple task for all sorts of valid reasons, anyone who struggles to understand this and gives you a hard time for paying needs to consider that other people have different experiences and circumstances than them (I know, shocking right?).
If you're not setup to do jobs like this, or you will worry that you will get it wrong then the extra cost is a cheap price for the convince, and more importantly for the peace of mind. If you're going to be riding and worrying about the bike then you've negated the reason for owning the bike, it shouldn't cause stress it should relieve it.
Do what works for you, do what makes sense for you, do what fits for you. Everyone has different situations, knowledge, and different financial positions. What makes sense for one person doesn't for the next, people who can't comprehend that have an issue, not you.