As far as price difference and quality I would say there is always a difference. You get what you pay for usually.
EKI: Good quality, if you have any other EKI folders, you will notice a difference between them and a "chinatown knockoff".
Tarani: Also Good quality, I believe manufactured by Blade Tech or they were anyway. They always do nice work.
Dionaldo: Also good quality, good finish and fit.
S&W: Low quality, good design. But cheap over all.
MTech: Crap/rip off artists
Spyderco: Always good quality though not always the prefered materials.
Custom Karambit: With any custom you are paying for several things:
1. Limited availability (knives made by one person means fewer made than with factory machines, this also means higher cost to the maker and makes the knives more desireable to the collector)
2. Attention to design and craft(usually)
3. The makers name and effort
4. Better materials (usually but not always, depending on which factory models you compare to)
5. More interesting designs in comparison to factory knives. That's why factory makers employ a lot of custom makers for their designs nowadays.
6. Soul: a handmade knife does have a lil' more soul than a factory knife. When you go to a show and see the makers hands all soiled and hard. Finger nails black with oil and steel. Scars from burning, cuts, etc. You know some sweat went into your knife.
7. Money wise, customs either will appreciate with time or at least you will get most of your investment back should you need to sell it.
Factory advantages:
1. More availability.
2. Usually more consistent with the grinds and profiles as they are computer ground and cut.
3. These days the bigger name companies are using the best materials there are.
4. They often employ custom makers for their designs so you can have a knife design that you've always wanted for less than the custom.
5. larger quantites mean cheaper prices in general. Though the prices are getting higher with the cost of everything rising in the US, they are still most often cheaper than the custom.
If you buy a folder, Stainless liners are fine. BUT, Titanium is better. Why? because when the Ti locking bar meets steel there si just a bit more catch as the ti is less slick than steel on steel. Or so I find. As well, Ti is lighter than stainless.
In the end, if you want in inexpensive "user" get a Factory knife. If you want something a little more high end with more design flair and some soul, get a custom. Or at least get a factory designed like or by a custom maker. I carry a few factory knives myself, and will switch to a custom whenever the need arises. Different knives for different days and different occasions and dress.