Budget authentics for m2l vapors:
UD Aga t5 for $10 at Triangle Vape. Very nicely machined and made with easy build. Its tall and kind of ugly, but its really not taller than a kayfun 4; it just appears to be. You really can't go wrong with this one. It even came prebuilt I think.
Original Lemo or Lemo Drop. You can find them for $20 now. They have a reputation as a cloud chucker, but the air can be closed all the way down to zero so its not true. Nice big build deck. Fantastic flavor. I've been using mine for 10 months and will never sell it.
hcigar HC Plus. $20 from Froginfog. You can't buy it in the US, which is a shame because this is an extremely well made RTA. Wicking is not quite as easy as the other two, but I would help you. There don't seem to be any videos out there in English, or that you can see easily what the builder is doing (I've checked). One or two airholes.
Focloud. $30 from VaporDNA. Build quality is not the best, but the flavor sure is. Single or dual coil, one or two airholes.
As for clones: kayfun 4, Taifun GT2 (very easy build and fill), Ataman II (just got this clone, and I have an authentic), Eviva-t clone is also now available (I have 2 authentics and love this atty), Erlkonigin.
All excellent suggestions, I've owned several of them. For simplicity and reliability I'll second the Lemo or Lemo drop. I'll also throw in the Billow V2. Slightly more complicated due to being dual coils, but well worth the learning curve once you have mastered general building. I started learning how to build on a simple Plume Veil clone dripper that I picked up from MFS for like 20 bucks.