Mini genitank is a decent and inexpensive choice. Exactly the same as the aerotank but not stainless steel. Standard dual coil kanger heads and adjustable airflow.
I second this suggestion. I think the mini is $12.49 at
mount baker. I haven't personally used the Genitank, but I have two mini Aerotanks, which, for my, compare favorably to my mini Nautilus. From what I read, reviewers found them identical in use. I was going to get the Genitank, except I found the Aerotanks on sale for $10.
One reservation: I did try it out yesterday on a tiny Evod battery I have, and with the relatively loose air flow, even closed up, I didn't think it performed particularly well. I use mine on a spinner battery and am happy with that setup.