A forged katana, as opposed to one ground out of some questionable piece of stainless steel, is very expensive. There are some very good makers out there. Look out for words like "simulated hamon line" that is always a pretty good tip off that it is not what you looking for. (I'm assuming in this post that your looking for a "real" katana) "Stainless steel" is also not a good sign. Anything that you know that is stainless (440, AUS, etc) fall into that category. Shaped handles, "simulated ivory", movie knock offs....I think you can probably figure out where they belong.
www.bugei.com has some and they have a pretty good reputation.
Slobodian (sp?) makes some incredible stuff, but I don't have his contact information.
What do you want a katana for anyways? They really aren't very useful in this day and age. You might want to think very carefully about getting one. Unless your in a class of some sort, it will end up in the corner or on your wall. And you will have spent a lot of money for a decoration.
Folders and Combat knives, your in hog city. Check out
www.bladeforums.com as well, there is tons of information there.
"You get what you pay for" definately applies here. Unless you get a really small folder you going to pay at least $50 for a folder. There are some companies that put out quality knives for a good price. Columbia River Knife and Tool, and BOSS knives leap to mind. They make affordable knives and are pretty honest about the fact that they are not making masterpieces.
Stay away from United Cutlery.
Tons of Quality manufactures around. Check out the Makers and Manufactures forum at Bladeforums, a lot of the top companies have their own forum there. Just write down the names and you'll have a good starting point.
Internet knife companies abound!
www.newgraham.com
www.cutleryshoppe.com
www.onestopknifeshop.com
www.888knivesrus.com
www.knifecenter.com
Are some with the best reputations.
Sites to find custom knives
www.bladeart.com
www.knifeart.com
www.arizonacustomknives.com
www.customknifedirectory.com
are good places to start
LEARN YOUR LOCAL LAWS!
Don't say that you weren't warned.