The prices on those chinese pens are tempting, but I've found many models crack at the screw threads between top and bottom sections - the plastic is obviously

The prices on those chinese pens are tempting, but I've found many models crack at the screw threads between top and bottom sections - the plastic is obviously thinner there, and usually just too thin, and barely last as long as a full refill of ink. So maybe you'll need much more than 30, or you could buy something actually good for 30x the price.