Video baby monitor

The other day, it was raining really hard outside and I have a 3 month old son and a small dog. My husband was gone at work and my dog really needed to go outside to pee. The problem is, he always needs to be walked around the townhouse development in order to do his business (he won't do it in the backyard). So I took him out while my son was napping inside (door locked and all that - he was perfectly safe). I only stayed outside a few minutes while my dog did his business, but I was super uncomfortable not knowing how my son was doing inside. So I'm looking for a video baby monitor. What's out there that's good, but won't completely empty my wallet??