I have a 50# Little Giant and could not make knives without it, since I mostly use large stock. I have spent very little time on a press, but it is the next major tool upgrade in my shop!!
It would be MUCH easier to build a reliable and efficient press than it would a power hammer.
The ease of interchange-ability of the dies on the press makes it a great advantage in a shop.
Don Fogg sells a manual for building a press that I think is invaluable for this purpose.
http://www.dfoggknives.com/hydralic.htm If you decide to build a press, please document the process, photograph it well, and come back and post it here!!!