First thing to understand is that if you want to make your own stamps you'll have to spend some (probably lots) of time learning how to create objects in a suitable 3D programme.
Kits - a great way to learn about 3D printers, but again will require some time to build and get working properly. Kits were a cheaper way to get into 3D printing, but some of the ready-to-go units have come down in price so the difference isn't as great as it once was. Plus, if you have problems building a kit you're usually on your own and will have to figure it out yourself.
Some people get good value from them, RockyAussie being one as he makes a lot of bits and pieces for his sewing business. Me, I've made a few odds and ends for my hobbies, but they're pretty expensive things if I look at the time and expense I've put in to it! That wasn't why I built one, however, it was just something that I wanted to learn about, and anything useful that I make is a bonus!!
Just don't expect to buy one and design and print a stamp in a few hours.