A few things to consider when ordering a custom knife:
Materials: Some specialize in certain materials, such as 51200, AEB-L, etc. If you want a blade made in a certain steel, you could approach a maker who specializes in that steel. As for the handle, you can give them an idea of the handle materials, but understand that the price will fluctuate according to how expensive the materials cost.
Design: You have ultimate control over the shape, but if they give a suggestion, you should consider it. Afterall, they get to hold it in the hand and use it before you do. They might suggesting a tweek here and there.
Cost: Don't expect to lowball someone. Get an understanding of their usual prices before you set your own price. Also expect to pay a non-refundable deposit when they start on the knife. I require half up front on all my orders to cover materials. It is not unusual for someoen to "forget" that they ordered a knife and not have the money when the time comes to pay for it. The deposit helps you remember your commitment.
Time: Expect it to take anywhere from a month to a year+ depending on how busy they are.
Satisfaction: If you aren't happy, let the maker know and he will try to make it right. If you are happy, then let your friends know so he'll gain more business.
Experience: There may be makers who produce wonderful bowies, but can't make a kitchen knife worth a darn. The kitchen blade is made completely different than any other knife. It requires Heat Treat before the bevels are gound, which takes more time, belts, and patience. Find someone who knows what they're doing.
Hope this helps.
Jason Wilder