What is "ridiculously expensive" for you?
I use a MyHD MDP-130 card, and you can get it at Buy.com for $142.63.
Buy.com - MyHD MDP-130
What are the specs for your mom's computer? I have a 1GHz P3, so I think that card is the only one that I can use - it uses hardware decoding, so the CPU doesn't have to do any processing. All of the other HD cards out there seem to use software decoding, so they will rely on the CPU a lot more.
Hauppauge has a HD tuner that looks like a USB flash drive, and it sells for $99. The computer will need at least a 2.2 GHz P4 or 1.8 GHz Centrino and a 2.8 GHz processor for analog TV recording.
Hauppauge WinTV-HVR-950
You do not need satellite or cable in order to watch HD programming. You can watch HD with an antenna, but depending on where you live relative to the towers, you may need an outdoor antenna.
AntennaWeb will tell you how far the towers are from your house.
The man I loved - the man who vanished - he never came back at all. But maybe he's still out there, somewhere. Maybe some day, when Gotham no longer needs Batman, I'll see him again.