Squeezing a tennis ball, or using one of those hand grip spring things will help to build up some wrist muscle. When I had a bad car wreck in 1989, and had some extensive hand damage, one thing they had me doing was the tennis ball thing. But as soon as all the surgeries were healed so no dirt etc., I found I got more out of milking by hand and built up more strength. The squeezing of the tennis ball and such did help.
Your arms and all will really ache for a few weeks. I went to milking with one hand, 10 squirts, then the other hand 10 squirts, and what ever else I could do to try to keep up a rhythm.... There is no real good milking machine that is "not so expensive".....the cheap kind don't last or don't do a good job and the cow will get mastitis.
What kind of cow and are you going to let her calf raise also? There are alot of ways to get around it and get your arms/hands stronger, while still getting the cow to produce what you want.