At the bottom end we have the RK-12 (this includes the Mic-Parts one and AK12 from Advanced Audio) and Peluso CEK12. I'd put the RK-12 above the CEK12 because the RK12 is great for $30 and the Peluso is terrible for $280. It's brighter than RK12, enough that Fox Audio Research actually had to use corrective EQ in their C12 build using the Peluso CEK12, it actually sounds more like a K67 to me. There's also the 797 one, which costs around $60. That would be my choice out of the bottom 3.
Then we have the Beesneez CK12 which also costs about $280 USD, and is leagues ahead of the Peluso, I don't think it sounds quite as full as the HK12 and CT12, but it's pretty close IMO. Then we have the Heiserman HK12 and Tim Campbell CT12. I think they both sound great, though my favourite is the CT12 by a bit.
I'd say from lowest quality to highest, it's Peluso CEK12, RK-12, the 797 edge terminated capsule, Beesneez CK12, HK12, and only slightly ahead IMO is the CT12.
3U Audio will be developing a CK12 capsule as well next year.
Using the top 3 you could make an amazing mic. Using the second to last and third to last you could still make a really good mic, but the presence boost will be broader than a CK12 because the cheap Chinese made ones are closer to K67 capsules so they have that rise starting around 1-2KHz. The Peluso has a very brittle sound compared to the others, including the Chinese ones, yet it costs about as much as the cheapest of the premium ones. This is because all of the actual machining is Chinese, and they're just skinned in the USA.
I didn't rank the Maiku CK12 because it's so obscure. It's was an improvement in the B2 Pro I put it in but I ended up messing up the PCB and just tossed it (really should've kept it though). So it's less bright than the current Behringer B2 Pro capsule, but that might not be a 797 one anymore. At any rate, I would say it's better than cheap K67s (and better than the CEK12).
FWIW Telefunken uses the RK12 in their cheaper TF51/AR51 mic. It sounds fine, but it's no CK12.
There are some other capsules like the Lewitt ones, though I'm not the biggest fan of the boost in the higher end Lewitts, and the one in the CAD M179 which is apparently made by 797. Though those are also not quite CK12 like, I think they sit between the tone of the C414 XLS and XLII personally.
I believe the Rode K2 is another edge terminated K67 design, and not a true CK12. Or just a tuned K67 like the Lewitt and CAD mics have.
Since you mention inexpensive ones, just get the RK12. From Alibaba if you can find one with a minimum order of 1. I'll post the listing if I can find it. The ones that Khron used were pretty closely matched from the factory. They're the edge terminated ones from iSK (the RK12 should be the same capsule). I'd advise you not to buy from WGTcenter they're over a month late on my RK47, and they didn't even ship it until almost a month after I ordered it, and when I contacted them about it they claimed it was sent on time and then mailed me the same tracking link I was using that confirmed it wasn't posted until the end of May. Yet they claimed to have shipped it around April 30th in an email they sent me. Filing a claim on PayPal if it isn't here by the end of the week. I politely pointed out it was a month late and that the tracking said it wasn't posted until the last week of May. And instead got a rather vague reply saying what I mentioned earlier. My first purchase from them came in a couple weeks and had free shipping at the time. Just thought I'd let you know that WGTcenter is a bit of a gamble. The person who replied to my email was less than helpful.
Here's the link for min order of 1 RK-12s
https://m.alibaba.com/product/60728083275/New-34mm-Large-Diaphragm-Microphone-Capsules.html?spm=a2706.7835515.1998800312.27.6dc960df1y1q3i