kodaif, I have a few questions for you:
1) Why the desire for lowest cost ciem? There are obvious disadvantages with a single driver over dual drivers.
2) What is your purpose for this lowest cost ciem? If it's going to be for working out, then I don't really see an issue as I use my Kozee X1 just for my workouts. If it drops and shatters or if cable pins breaks off and gets permanently stuck, not that big hit on the wallet, relatively speaking. If it's going to be used for a gig and/or main listening pleasure, I would suggest going up at a minimum to a dual driver.
3) Since the process is the same regardless of the cost of the ciem, if you decide to "upgrade", it'll cost you more in the long run as resale value of any ciem product is huge. Unless, of course you plan on having more ciem than a dozen eggs, which a few members can proudly claim (you know who you are).
4) Do you know what to expect from a particular model? Sound signatures are all over the map, even for single driver BA ciems.
Yes. I concur with average_joe, Ineaz and Alclair are good and reliable sources for what you may be searching for as I've done multiple business with both companies. Like Kozee, read up and be cautious over other companies that may cost you a lot of time and headache.
Good luck.