Have to agree, I have 4, under $20 each (surplus), so maybe $30-$40, retail. Also come with a universal remote, as it also relays remote signals wireless. Works great with my video security system, have remote monitors in 3 rooms, and about to add a fourth (bathroom).
I bought a kit years ago, took a lot of tweaking to get a weak signal on a TV, wasn't very stable either, only about 30 foot range. Complete waste of time and money. I've got better test equipment now, and could probably get better performance, but it was probably not a great design to begin with, kits are often like that. Most anything RF is better pre-built, and cheaper too, unless you have the knowledge and equipment to tune the circuits.