Trundle Bed

the playroom/guest room is now chloe's room. we got rid of the futon and now just have chloe's twin bed in there. we want a trundle bed but are having a hard time finding one.

i love the look of this:

but i want one that can pop-up into a king-size bed so couples can sleep side by side. (would it be weird to put up a couple in a multi-level bed?)

this is all i can find. seems kind of expensive ($399).
any ideas?