Just like anything and everything else in vaping, what can be considered to be "outrageous prices" is also...subjective.
Take Five Pawns' juices as one example. They sell a 30 ml bottle for $27.50. That's nearly a buck a ml. I don't mind paying that at all because I really enjoy their Queenside flavor.
Now, if I didn't want to pay that and decided to DIY, the start up cost to me to buy all the supplies and safety equipment in order to do it right, the ingredients that I waste on trial and error in order to get the same flavor...but most of all the sheer amount of time it would take... I don't know about you but that kind of time I don't have. I also don't want to put that much effort into something that I have no interest in (making my own juices). Therefore, that price? It's a pittance as far as I'm concerned. I'm paying for much more than just the ingredients.
I'm paying for convenience. I'm paying for my time, which to me is worth more than the mere $27.50 a bottle.
It's up to each individual what they want to pay and what they deem worthwhile...or not. If you want to DIY, go for it. Me? I prefer to find my favorite flavors and pay the vendor what I feel it is worth, the price(s) the market will bear. Since these companies are successfully selling their product, I'd say the market is bearing their price(s) just fine. And that's just my two cents.