I can somewhat understand someone who is not mechanically inclined wanting to have a professional assemble their lower (or any other gun/part) so they know that it's really done right. As an automotive mechanic, I see horrible quality "repairs" performed by people all the time who have absolutely no clue what they're doing, yet try anyway. And since a firearm is a potentially lethally dangerous machine if things aren't done right, it's understandable to not want to risk it.
Now, having said that.. the internet is an absolute wealth of information, videos, writeups, etc. that can help you lewrn how to do it yourself. And as others have said, the tools required are very inexpensive. The lower is also a pretty simple device to put together. Just requires a little care and patience. I'd watch some videos on how it's done to familiarize yourself with it, then give it a try yourself. You always have the option to stop if you get to some part you're not comfortable with and seek professional help with it at that point.