Dave,
Well it all depends, does someone want one to look like a particular type plane and fly well or does someone want it to be scale, and harder to fly? ( a thing called scale affects when you make it smaller then full size plane) I use to build non-scale planes for people and would average about $.15-.35 a hour! But I did it for kids and begginers Most people don't like the true cost to build them! Just like a hotrod. It's cheaper to buy a built one, then have one built!

If it's a scale plane, I have find & read books with lots of pic's order a kit that is close to what I want, and customize it till it the true shape & size. Then I have to find out if they make the retrack landing gear, or do I need to buy a set and rebuild them to be right for the plane I'm building ,They don't make them for all planes. I paid $300.00 for the set for my F7F Tiger Cat. and thats only the gear it self, not the parts to make them work! I then have to mount motor and the servo's and radio stuff and make sure it all works smooth and the gear work right also, build the cockpit and instruments.
I build the planes out of Balsa wood, then glass over it with I/2 oz cloth and use epoxy, not poly(no stink venting, or wax to remove if you can't get with out) then sand it smooth as a baby butt & straight! Then mount the engine cowl, and cut what ever holes it needs,then paint everything with auto paint, I don't use decals, I hand paint them on. then clear it with gloss or semi gloss, or flat, which ever it calls for, then set the center of gravity on the main spar (back a little for stunt forward a little for smooth flying)

I guess it's like asking you how long and how much to build your Camaro, before you started. You have built many, but not the Camaro yet.

A scale plane can take a easy 4-6 months (I don't work on them 24-7, only evenings & week-ends, just like a car. I work days to pay for them ), and a trainer can be built in 3 to7 days. I have built gliders in about 36 hrs