I don't have much experience in kitless pens yet, however I'm working on developing my own style. With the amount of time and tools and material and knowledge required to make one, I'm looking at starting somewhere around $100. I mostly make rings, not pens, but I do a lot of what the others are saying. Search competitors sites. Find their pricing. I don't know that many kitless pen makers yet, but everything I'm seeing that is of good quality goes for between $100-$300. All of these are fountain pens. The difference in material is usually what marks up the price as I'm seeing, and then followed by the difficulty of design that goes into the pen, and also the experience behind the maker.
In the ring world, it irritates me sometimes to see a ring that can be made in a few hours from $50 of material sell for $400-$1,000 but then again no one is forcing anyone to pay that fee, people are doing it of their own accord. I did a lot of comparing prices when I recently started getting into damascuss and found that most damascus hand made rings sell for $350+. In a way I feel like I'm low balling myself for selling them at the $200 area, but I I feel happy to let it go for that price, and I also feel like I'm giving the customer a good and reasonable deal.
So that whatbit comes down to. What would it take for, let's just say me, to have you make a kitless pen? What would you be willing to let it go for? Is $75 enough to make you feel good? Or is $150 more your speed?
Also since you have a customer already lined up, ask them what their budget is, and try to keep it a good margin under their budget if you can, while still delivering a quality piece. The tad bit that they didn't spend of their max budget will make them happy because they still have money left over, and if you deliver something of great quality with that bit of savings thrown in on top they will be ecstatic!
Example: $75 budget, put $65 into it. $100 budget, put $85 into it. $200 budget, put $170 into it. I find that usually keeps the customer happy, and keeps them coming back for more because they know they are going to save a bit off of their percieved value of your work, and also get something amazing.