Through our Lonely Planet, we discovered that a lot of the cheaper motels were categorized as Love Motels. We had heard of these, as they are prevalent in Japan where they are used by unmarried couples wanting a few hours "rest" away from their parents. In Japan, the rooms have interesting themes like "Hello Kitty".
In Korea, although perhaps the rooms might be used for the same purpose, they seemed a lot more like just a regular motel room. In a couple of the love motels we stayed in there was some interesting movies on TV, and in case that wasn't enough, a VHS (!) collection in the hallway outside. Other then that, the love motels mostly come with hairdriers, shampoo, perfume, and mood lighting. Strangely though, none of the hotel rooms we stayed in on our whole trip had what we would consider towels - they were hand towels, at best. We were happy to have our own pack towels with us.
It's almost impossible to make reservations at love hotels - the owners usually don't speak English. There's no receipts, no helpful directions - just a tiny hole in the front room through which you pay and get a key. Sort of strange - but at $30 a night (almost everywhere) they were the best way to get a clean, cheap room. We didn't see any strange people around - in fact we almost didn't see anyone at all - and there was no unusual noise coming from any neighbours. The love motels are usually very well located in downtown, and can be seen by a symbol on their sign.