Does it come with the keyboard dock? You can pick up a refurbed tablet for $250 and the dock for $80-90, so maybe offer $200 for the tablet and $75 for the dock.
The Transformer doesn't have the issues the Prime does.. the Prime was a bit of a flop because of the aluminum chassis and wifi interference.
I love my Transformer.. I don't use my laptop anymore, I don't have an insane drive to mess with my phone anymore, and I use my desktop about 50% less. The Transformer is built pretty well (far better than the plastic tablets from its generation). The CPU is very quick and the GPU handles most games pretty well (PSX emulation is pretty good!)
Its a solid buy for a bargain price