I bought the 8gb for £2.80 yesterday price seems to have risen most likely because people were buying a LOAD of them.
Probably the cheapest prices i have seen.
I would never buy anything like a class 10 card from eBay unless the seller was someone like eBuyer or Argos, so many fake cards on eBay.
Better to pay more and know you are getting class 10. Also the class doesn't mean a hole lot, read and write speeds are what you should look at.
It happened to me to find micro sd cards not respecting class written on them. there are a lot of softwares that mesure writing and reading speed. Personally, I would spend a little more money for a good product i.e. I have a 32Gb Samsung, Class 10 and I payed it 35€ (shipping included..)
If you don't need a big capability, a good 8gb or 16gb can cost you not more than 10-15€...
It's something you buy once and least for year..buy it good and you won't regret it!