So i have an Iphone 3G and I feel like upgrading it so yesterday i looked and noticed a lot of android phones free or under 100 but today i look and everything that was free yesterday is .01 - 20 dollars today? why is that?

I've had my Iphone 3g for 2 years and 5 months

Any suggestions to which phone to upgrade to? With reasons and price to?

Thank you - Logan