if you can afford it go for the biggest one. The expression. Ebay really is your best place for price, You have to be willing to bid on a few to get your best price.but look around as there are some places that have bundles with 4 cartridges for right abt $300.
There are 3 machines now.... Michael's has the exclusive on the Cricut Create which supposedly is the size of the baby bug but has a lot of the same features as the Expression. I've seen it at Michael's but I don't know a lot about it.