We forgot our regular monitor (one of those $100 Fisher-Price ones) at home when we went to visit friends for the weekend. We went to Wal-Mart to pick up the cheapest monitor we could find just to get us through the weekend and then keep in the trunk for whenever we go places.
The Safety 1st Crystal Clear Monitor cost us $20.
It actually is crystal clear!! I could not believe it, it is so clear that you can hear the hum of the furnace through it! There is no feedback either - no annoying hum that all monitors seem to have!
The receiver can be plugged in or has room for a 9-volt battery so you can take it with you when there are no plugs available. Not sure if plugging it back in will recharge the battery or not. It has 2 channels and a great volume control.
For $20 I seriously could not recommend a better monitor.