Well, I'm not going to say how much I charge per hour...but if you run it purely as a business, then you have to think about all your overheads - machinery costs/upkeep/replacement, electricity, insurance, materials and consumables, accountancy fees, website/etsy fees, etc, etc before you even start thinking about paying yourself a wage. Plus also remember that, if you're running a proper business, the wage you pay yourself should be different to the profit that goes back into the business. Also don't forget that you don't get paid holidays or sick days if you work for yourself.
So, let's say that you want to earn an average-ish wage of £24,000 a year - that's £500 a week, worked over 48 weeks (lets say you have 4 weeks holiday/sick a year), after all your expenses have been taken out. £100 a day. How many pens can your realistically make in a day? 5? 10? And don't forget that you need to include time to make them, photograph them, list them on etsy, answer numerous emails, do your accounts, order new stock, pack the pens up when they sell, take them to the post office, answer more emails, etc. Now how many pens can you make in a day? Realistically, day in, day out? I don't know that answer to that, because I don't really make the type of pens that you're talking about, but I do know that doing all of the other stuff takes me more time than making the actual pens :-( So, let's say you can make 5 pens a day (25/week, 1200/year). You need to price them at £20 each PLUS the cost of the materials (lets say £8), PLUS the cost of all your expenses for the year divided by how may pens you make a year (so lets say your expenses per year average £2400, that would be £2 per pen). So, we're up to £30 for a pen by now. And then there's profit....how much profit do you want to make to be able to grow your business, invest in better/new machinery, market your items, etc? It's not an area I'm that familiar with, but Walter has written a fair bit about it, I think.
And then you have to think....is £24,000 a year enough to make it all worthwhile? You have all of the hassle and uncertainty of running a business for a fairly average wage. Is that enough? How many business owners do you know who would be happy earning £24,000 a year?
Second question is, even if £24,000 is enough for you....can you actually sell 1200 pens a year? If you can only realistically sell 600 a year, then you're going to have to double the amount you make on each one just to reach your £24,000 goal, or do something else in addition.
And finally I will say that I certainly don't practise what I preach - it's almost impossible to in the early days of starting a business. 
