DIY can be MUCH cheaper, but there is definitely an art to it.
the math isn't so hard, especially when you use 100mg/mL nic concentrate. There are DIY calculators out there for both android and iOS... Biggest thing, IMO is do not screw up the nic level, and make sure you purchase from a reliable source. I get mine from Wizard Labs and have been nothing but pleased. You have total freedom... And for around $80 I can make some ridiculous amount, some 2000+ mL... So what, like 40 cents per 10mL bottle
Flavoring is an art though, like I said... When you buy from a vendor, you are paying a lot for intellectual property in the form of a recipe. IMO it's worth it to buy from folks like Alien Visions and Heather's Heavenly, and several others, cause they have some knock out flavors. But if you want to dabble in it, and stumble upon an excellent recipe, the cost savings can be remarkable