I think all new machines come with a foot pedal. Some also have a button option (on the machine) that you can also use.
The older machines in cabinets often had a knee controller. All this was the foot pedal mounted inside the cabinet, and a knee lever on the cabinet so you could operate the foot control with your knee.
Sewing machines are so personal, I think it's very tough to buy one for someone else.
For $800 or under, I'd probably look at Janome machines or possibly Sears Kenmore (which I understand are made by the same company that makes Janome). Does your mother like taking a machine to classes? If so, there is at least one full-featured Janome that weighs only 12 lbs. Try going to the top of this board and doing a search on Janome to find threads about specific models. Also visit
http://www.patternreview.com to find multiple reviews of each model; these tend to be very informative.
Be sure the machine you get has the needle-down feature.