There's custom, semi custom, and production. And some individual makers do all three!
Here's where I stand on some of it. And I've been thinking about this a lot, since there's a push in the household to get some other people involved in stages of the knife making. Koyote girl already rocks on sheaths, the other family in the house has a knifeknut mom who would love to get involved in some of the grinding and finishing, glue ups and such....
Anyway- Full custom is just that- full custom. You can work with the maker's artistic and creative sensibilities, like Tai Goo, or submit a design and find a maker who will do Exactly What You Drew. Personally, I don't like the latter. I'll work off of a design, but there's going to be things going into the knife that are all me. I'm going to have to tweak the balance, edges, feel. Rarely do drawings translate 100% into reality with perfect results.
The "send me a check (after I have a heat treated blade done) and tell me what kind of thing you want" works well for me. Surprisingly well, given that I'm only 2 years into this. I just mailed one off to a WSS regular that went that way. He asked for something about the size of the lacewood scandi wharnie i have up for sale, but more like my BC style. So I started it, he paid me, and today it's in the mail. I gave him a preview pic after making it and it's like telepathy!
That's custom- sometimes it costs more, sometimes it doesn't. Oh, you can get a leuku or puukko for under $30, but for the stuff you get out of a custom, you can't really beat the pricetag. Mind, if I was uberfamous and had a 3 year waiting list and made perfectly finished exotics, I'd be charging $500 a knife! But even then, you wouldn't be able to duplicate it in a production knife- at any price.
Production- okay, I'm inordinately proud of the sheaths coming out of the shop- but production knives generally can't beat the edge, sheath, and finish work of a decent handmade knife. You get quantity, consistency, ability to easily replace. And there's some damned good production knives out there. Some of which came out of custom shops that went production. Not a problem. The smaller shops are still semi custom, sometimes.
Semi-custom. This is where the individual maker shines. I'm gonna talk about me, since I don't want to put words in Andy's or Scott's, or Bryan's or Rick's or whoever's mouth. But I think I'll get some agreement out of them
The semi-custom knives are what production knives can't be, in a few ways. Generally you get a better sheath, can request a sheath for horizontal carry, piggyback, left handedness, or oven a full flap cover- you can't do this for a production, and a custom sheath is going to cost an extra $30 to $75 easy.
The semi-customs are most often models or designs the maker has come up with- often with influence from a target group. The production knives HAVE to worry about a larger market. I don't. I can come up with quirky but savagely effecient designs that don't have "walmart appeal". Oh, I need to sell a couple dozen knives a month to do Well- at my $70-$160 normal price point. If I was doing $160-$250 I could cut that back some, I guess. But I can afford to tune and tweak and produce a design like the leuku pattern bushcrafters, or the (yes, I'm making more) shiny woodcraft EDC and do 4 or 5 a month. That makes for a much broader selection for YOU, the user.
The semi custom also has options- kinda like a custom rifle. You use a production recevier, and go from there. I've usually got 2 or 3 of any blade type I make often around as blanks. You can ask to buy a blank, select a handle material, custom order the sheath, get a scandi instead of a convex, change the blade length or handle. When it's a choice between a $70 production field knife and $120 for a semi-custom field knife, there's no argument! You get that much extra value from the sheath and the right edge profile alone. And- with many of us- you know the blade has cut, been stropped, tossed into a stump in a full force throw, and maybe even batoned a 2x4.