Everything is like over 1k. I looked at Netguardian and a few others, but they're pricy!
The Arduino board was like 30 bucks. If I need more inputs (like double what I have) I could get the "mega" version which is still under 100 bucks. So given this is custom hardware I pretty much have to write the software for it, but it will be pretty simple.
There are some open source options. I've been toying a lot with this sort of thing recently and have "almost" settled on http://domotiga.nl/ it has a whole bunch of modules for hooking into various types of device (I guess massive overkill if all you intend to do is monitor a few environmental bits... but I wouldn't be surprised if you find yourself in a similar position to I- wanting to pull power consumptions, network usage statistics, filerserver stats, sonos usage, and just about anything else with a pulse!