Eh? You can buy packs of 5-10 in the UK for under ?4. And there are probably even cheaper options if you're prepared to use eBay instead of an actual retailer.
I don't think a pencil sounds like a good idea. Something soft that doesn't risk leaving a mark would be better.
I use pencils, pens, my finger and things like that too. My screen is dirty and disgusting, but that's because I have no screen protectors and I drop my 3Ds on occasion. I don't recommend it unless you're like me and getting an XL soon.