There is a seller in Ukraine that sells radiatio0n detection tubes and what not on ebay. https://www.ebay.com/sch/i.html?_ssn=dosimeters_radiometers_counters&store_name=dosimetersradiometersdetectors
I bought a SBM-20 geiger tube based kit from them years ago. Plus I have an alpha, beta, gamma detecting tube only here I bought from them, but not yet done anything with.
I fact did contact ukrainian Ebay seller and he told that chinese Geiger counters are not sensitive enough. But not sure if he wasn't just trying to push his product. He had some old looking, soviet Geiger counters. SBM-20 is just a tube, what is ready Geiger counter I could purchase?
Here is a list of dosimeter he recommended:
Now to the essence of your question.
If you want the simplest possible dosimeter, then I recommend you the IRA-01 dosimeter:
https://<a>
www.ebay.com/itm/195745152485<;/a>
Or keychain-dosimeter Biri:
https://<a>
www.ebay.com/itm/195729586117<;/a>
If you want a more advanced dosimeter with an LCD screen, then I recommend you:
Master-1 (with one counter):
https://<a>
www.ebay.com/itm/196052505949<;/a>
Bella (with one counter):
https://<a>
www.ebay.com/itm/204286573017<;/a>
Jupiter (with two counters):
https://<a>
www.ebay.com/itm/195838368013<;/a>
Anri Sosna (with four (!!!) counters):
https://<a>
www.ebay.com/itm/204552612344<;/a>
If you want a dosimeter that will definitely help you survive a nuclear war, then I recommend you a military metal dosimeter ((with four (!!!) counters):
https://<a>
www.ebay.com/itm/204282870751<;/a>
If you want a dosimeter that can measure both gamma and beta radiation and is quite cheap, then I recommend Pripyat:
https://<a>
www.ebay.com/itm/204277500290<;/a>
And if you want a dosimeter that measures both gamma and beta radiation, calculates the accumulated dose and sounds an alarm when there is a dangerous level of radiation, then I recommend you Terra-P plus:
https://<a>
www.ebay.com/itm/204259641715<;/a>