I agree with just using cheap, disposable 510 atties and even 510 carts will work when you pull the stuffing out of them. This is what my local B&M store does to let customers "sample" new juices and it works well. Buy them in a 5 pack and/or look for sales and you can usually find them for under $2 each.
That said I love my RDAs.
I have a handful of very cheap Phoenix clones that I bought from Reosmods (currently out of stock). Out of the box the coils aren't usually optimal and they have a tighter draw than I generally prefer but they don't leak as much as some other RDAs, hold at least 10 drops (when dry), and are small enough for "stealth vaping". All metal construction means they are safe for the "plastic eater" juices out there too.
I also have an A7 that was more expensive (under $20) that is better made and easier to recoil. It draws air from the center of the atty, below the wick, and provides probably the best flavor out of all of my devices. About 10 drops.
I just bought an Igo-L. VERY well constructed, a large platform for thicker or dual wick/coils (if you like) and a pretty good bargain for around $14. I drilled the air hole out from 1mm to 1/16th inch (1.56mm) and it vapes like a volcano. I do think it is funny that they made it like 21mm in diameter instead of a standard 22mm so it looks just a *tiny* bit too small on top of a Vamo or the like. Other than that, a very good RDA.
My "go to" (vaping it right now!) is a Smok RDA "Octopus". About $8 if you shop around. This is my favorite dripper by far. Out of the box I found the o-rings too loose and the wicks too long (gives dry hits even though there is still juice in the wicks). I replaced the o-rings (a bit of dental floss under the stock o-rings works too), busted off the tip of a toothpick in the air hole under the wick, to help prevent leaks, and drilled a new 1/16th airhole in the last groove near the top, which is easy to do since the cap is made of aluminum, not steel. Some easy improvements can make this good RDA *great*! Fairly large platform for thicker wicks/coils AND it has both holes in the posts for securing wire as well as knurled thumb screws for tightening, both things that I *wish* the IGO-L had. If they start offering these in a polished stainless steel I'll buy five or six more.
A friend of mine beat me to the punch and picked up an AGI before I did. We finally got an SS wick rolled for it and it works as well as either of my AGA-T2s do now. In dripper mode, without the tank, it's EXCELLENT. Extremely well built with a huge platform to work on. Just a bit spendy just for dripping at around $40.
Probably more than anyone wanted to read about my opinions on drippers but hey, there you go
