Ant Setchell shows how to convert a welding clamp into a fret press. To make the press you have to modify the jaws. The top jaw holds interchangeable fret cauls from Stew Mac (to match the fingerboard radius), the bottom jaw is a padded caul to press on the back of the neck. You would pay over $200 for a handheld fret press, but a welding clamp will cost you less than $15.

There are a few different ways to put frets into a guitar neck. Most of them involve applying pressure to the top of the fret. You can hammer them in with a small hammer, but you might expect better results with the even pressure from a fret press. The link below shows an example of a home made fret press.