On a low budget you're going to be limited to 10x2 or 12x3 trapezoid leadscrews with a delrin nut. With 300rpm and a 12x3 the maximum traverse rate is 900mm/min for rapids, maybe 1/2 that for cutting. A 600mm axis will take 1.5min to traverse.... so this isnt going to be a fast machine! You may wish to make it smaller as a starter machine...