For me, it is also the $$$. It is not that I save much with DIY, but I get to spend it differently.
First off, you probably should plan on spending about $200 to have a shop do a good service of your regs, including parts and S&H.
And you can get started for quite a bit less than $800.
BUT, it is probably not going to save you any $$$. I probably spent about $200 for a book and initial tools (it did not take much more than I already had for cars and stuff) and the first batch of parts. What I quickly found was that my regs went much more than a year or two between servicing. But I still spent much more than $800 in the first couple years stocking up on service parts when the price was right and buying more regs ($30 per stage plus $5 to $20 for parts). While I strongly recommend a backup regulator as the best way to prevent regulator problems from having a negative impact on an enjoyable dive trip, a single rig, well cared for and competently serviced when needed will suffice if you are not interested in DIY. Even now, 15 years since starting, DIY does not save me $$$. But, rather than spending it at some dive shop for labor, I see a good buy on another BP/W or even another regulator I don't need but can't live without.
If you are not interested in DIY, then don't do it - you probably won't do it very well anyway.
If DIY does appeal to you, don't expect it to save $$$$. Do expect to actually spend more $$$ on gear as the bug takes hold.