I took to grinding my own. 5/16" HSS blanks are inexpensive, and a well-made HSS tool cuts better than most carbides. I actually bought carbide insert holders, went back to HSS, and now only use carbide when I work on the steels I hate most.
My advice is to buy or make a quick-change toolpost, a bunch of holders, and use 1/4" HSS bits for everything. I do that now, and I've moved to a machine that will handle 1/2" tooling.
I still have the plans for the style I made. $50 for the material and tooling (when I bought it) and a weekend got me the post and a few holders, and was made completely on the mini-mill.