After building a PC for the first time a few years ago, I'll never buy a pre-built desktop again (low or high end)
The amount of corners they cut and terrible design decisions they make just so you can't reuse the parts elsewhere are not only criminal from a consumer perspective, but an environmental one as well
I get your concern, I was extremely worried my first time. It's a lot easier than you might expect though
Still, it's your money and your comfort. If it's worth the extra money for a pre-built to save you peace of mind, by all means do as you will