Timken is just a brand name, as is SKF, Fafnir, and a couple of others. The price difference should be mainly in the grading of the bearings, as far as fit. High precision bearings, as are expected in machine tools do typically cost quite a bit more. Depending on what type of work you want to do, it may not be worth it. As long as you can afford it, get the precision bearings. Otherwise, do the best you can.