The most important thing about Baseball Field Chalk line Markers:

Good dry line chalk markers all tend to do the job but cheap junk tends to be made too lightweight for frequent ballpark use and abuse. Many rust prematurely, clog and just do not drop a consistent thick chalkline. So, you could be replacing them sooner and ultimately paying more than you need to.

I wouldn't sweat capacity, 50 LB models are plenty for all but the busiest fields. But I would strongly consider the soft, no-flat tire models for a few good reasons. I only recommend 2 wheel models where budgest is an issue... I find them to difficult to draw straight lines, even before beer 30.