roach motel

Etymology
The meaning "low-priced motel" is because such a place might be expected to be infested with roaches. The meaning "something easy to enter, difficult to leave" is from American roach-bait brand, advertised with the slogan "Roaches check in, but they don't check out!"

Noun

 * 1)  A low-priced motel in a state of disrepair.
 * 2) Something that is easy to enter, but is difficult or costly to leave.