I've ordered a couple of linear pots for testing. If I can hook them up to the brake cable and they don't require too much force to operate everything is fine. They're quite affordable as well.
Strain gages would be nice as well, but I have my doubts regarding reliability. These things need to be properly glued to a surface and covered up well. Definitely on a bike that gets wet and will see quite a lot of dirt / salt in the winter. Otherwise Mr. Oxi Dation would take care of them quickly. And I don't have a cheap source for them as well, as I don't need 1000s.