I’m not familiar with that specific doser, but assume it is a peristaltic pump doser. The best tubing for this application is silicone tubing….it will last the longest and have sufficient resistance to the alk, calc or mag you are running. I only wish my replacement tubes were only 5.99. If you wish to purchase your own tubing (and if need be, attach it to the end pieces with electronic welds) go for it. It’s readily available from many vendors with the caveat that you will need to purchase somewhere in the area of 15 meters.
I’ll just stick to having to pay $10 - $12 every X number of years for a short piece of tubing. (I haven’t had to replace mine yet….about two years.)