In short, yes, you'll want to buy a yalm. It's a lot easier to level on rubi-ka than it is in Shadowlands at this point in time and you'll need a way to get around. You'll find that 5 million really isn't very much money if you just save up :)

Eventually, you won't need it that much anymore. You'll be able to instantly cast parrot, a nano that turns you into a bird that allows you to fly on rubi-ka and move along the ground very fast in the shadowlands. While you won't need a yalm much at this point, you'll also be around lvl 125 or so before this happens.