Scheduled Load Balancing With Multiple ISPs?

Friend of mine has a setup out in the sticks, currently with two ISPs: Hughesnet satellite, and a line-of-sight WiFi provider; they're also getting a cel tower within range soon and he's looking at adding an HSPA/LTE connection via that as well.the first gives him a static IP and ridiculous speed and bandwidth at night... but far less speed and a painfully low bandwidth cap during the day (you go over, you pay through the nose).

The second gives lots of bandwidth but poor speeds (difficult to even watch a YouTube video) and a constantly-changing dynamic IP.The third, once implemented, will give him good speeds and decent bandwidth (I believe up to 10GB/mo) but again, will get spendy if he goes over that limit.Right now, I've got him set up with both routers plugged into the same network, multi-homed the NICs on his machines (192.168.0.* for Hughes, 192.168.1.* for LOS) and a little script on each computer that will change the default gateway to let him select which ISP he wants to use... however, it's going to get trickier with a third, and will make it even tougher to keep track of the bandwidth used on each one... especially with multiple computers, a DVR, and two users.

So I'm looking for some way to automate all this... something that will, say, use the HSPA feed most of the time for his whole home network, switch to LOS if it gets near the cap, and switch everything over to the satellite automatically during "unlimited" hours. Again, I'm not opposed to setting up something PC-based with the appropriate software, although for my own sanity, it would really need to be Windows-based (I'm way below n00b with Linux).