Have you thought about getting one off Trademe? I've used about 3 different baby monitors - I've used the standard analouge ones (Philips and Tommee Tippee) and the digital one (Avent). The digital one is definitely best for clarity, but from what you say, the analouge ones would do you fine. I didn't notice any difference between the Philips and Tommee Tippee monitors. You can pick them up for about $20 if you look out for a bargain. And, if you don't like it you can always sell it again
Oh, if you want to take it out into the garden a lot, one with a rechargeable base might be handy - will save you buying lots of batteries.
ETA: From memory my philips rechargeable one was $30 on trademe which was a bargain, I think they usually go for around $50? It's been a while though so I may be wrong!
Edited by amykt