You will get as many opinions of what a guide knife should do as there are guides. For me, a guide knife should do many things well. It should be at least adequate as a camp knife for whittling tent pegs or cutting line. It should be an ok cooks knife and skinner. It should be a decent survival knife just in case And it should be able to be sharpened in the field.
I'm with those who say buy a cheapo fillet knife, and I would never say a fillet knife is a guide knife, IMHO. So attached is a pic of my favorite that I made. The prototype was tested in the Aleutian Islands by a kayak guide, and it got rave reviews.
It is 1/8" 154 CM, with a red linen Micarta handle, 8 3/4" tip to tip, blade is 3 3/4. Handle has a good finger groove, and could be used with light gloves.