Making your own knife is a great idea...if you have time. It's always something I wanted to try but with work, family life and the usual hussle and bussle when I get some spare time (not all that often with a 2 & a 6 year old boys) I like to just get out out of the house and have a wander with the dog, or sit quietly outdoors and watch the world fly by.
If you can't or don't fancy making your own knife right now then the Frosts Clipper is a really good place to start. For sale widely on the net for around the £10 mark these are really good first knives to be using for bushcraft. As stated above two blade materials are available. I own a Carbon one, and to make it that little more interesting I purchased a leather sheath from ebay which has a fire steel loop. It cost around £20 but I really do prefer it to the platic one that comes with the Clipper.
I'm sure that many knives are relatively cheap and good for practicing bushcraft with, but many, including myself went down the "Clipper Road". I certainly wasn't disapointed.
I also own a Fallkniven F1, more costly at around £60 but well worth the money in my opinion. I use the F1 as my main fixed blade but always ensure the trusty Clipper is packed away just in case.
Hope this helps....ATB....Stu