Well, lets see,

When I lived in Kyrgyzstan, it was possible to fit refilling valves on disposable lighters. And it was very cheap. I guess, it should be still possible. I see how you can make a similar lighter - use a lighter with transparate gas container to see what is inside, cut some part out of it, glue plastic bottom and then fit the valve. I do not know if my father be ready to make a lighter for $20 for you, but I can certainly ask him, he has plenty of time to make knives (He recently made me and my brother knives based on Ray Mear's knife, http://www.raymears.com/shop_item_desc.cfm?id=72&itemType=Cutting%20Tools, but with thinner blade for convenient cutting, a bit different but very convenient grip and longer cutting edge, extremely sharp, though the steel is the problem - even though it is sharper than my Busse, unfortunately it is very brittle).
What do you think about these lighters? I was looking for a low-cost lighter which I could put on my keychain. Finally, I found these two lighters:

http://www.everyonedoesit.co.uk/online_headshop/Blue_Karabiner_Lighter.cfm?iProductID=2775
http://www.everyonedoesit.co.uk/online_headshop/Turbo_Flame_Lighte_Stick.cfm?iProductID=2363

I ordered myself Blue Karabiner lighter - it looks more solid though not that hot.