It does depend how you view your skills. How long does it take you to select a blank, cut it, turn it, finish it, press it together? If you were working for me turning pens how much would I have to pay you per hour?
The way I look at it is that I pay the cleaner £10 per hour so I certainly don't want to earn less than my cleaner, if a pen takes an hour to make then that is £10 minimum, then there is the cost of the kit plus a markup of 50% as I have had to outlay the money for the kit, same with the blank, pen box, whatever abrasives and finishes are used, electricity, partial cost of machinery, blades, tools etc.
In this example if I was paying you £10 per hour to make a pen I would still have all the expenses after I paid you, so I would have to add more for the profit I want to make which is 100% minimum for me. The amount of profit you want is up to you, but profit is not part of the cost of making it, so how much you pay yourself per hour is a production cost just as the cost of the kit is.
It doesn't end there, if you make a fountain pen it has a higher perceived value than a rollerball or ballpoint, it may not cost more to make or very little more, but the perceived value is higher so add at least another 100%, but if it is something special then just pile it on. It will sell or it won't, if you have people who want to buy your pens then charge them the price you want to sell it for.
If you are just funding a hobby then you don't need to earn anything per hour and don't need to make a profit or not much of one so you should be able to sell by the ton. If you sell cheaply you will become know for selling cheap pens.
Peter