[1] https://www.microchip.com/en-us/products/clock-and-timing/co...
[2] https://www.teledyne-si.com/en-us/Products-and-Services_/Pag...
If you're interested in a small atomic clock and don't absolutely require the very low power consumption of the SA.45s and the very small package size you can get better performance, reliability, and cost in something a big larger and quite a bit higher power consumption.
The CSAC improved atomic oscillators a lot more in power than size... but its timekeeping performance is so/so as far as atomic clocks go.
In particular, the surplus market has a lot of telecom rubidium that can be had quite inexpensively.
I'm personally a fan of the PRS-10 (which also exists in a benchtop form, the SRS725). They seem to regularly sell on ebay for about $300 with a little breakout board for power. And unlike many small rubidiums they have very good phase noise. You can sync them to GPS time using a 1pps input (though I believe on the bare modules the 1pps sync is optional so if you want to use it be sure to get one that has it).
I searched on Mouser and found that part no longer has a listed price; there are fancier chip-scale atomic clocks from the same company, the only one with a listed price going for $3,528.23.
Others from a different manufacturer are just over $2,000. A kind of awesome thing is that one of those chips is marked
Frequency 10.000000 MHz
It's awesome that that's not just an estimate or some kind of exaggeration!
Timekeeping of atomic clocks is still waaaayy better than next-best technologies (like temp-compensated Xtal oscillators). And size/power/$ constraints matter. So CSACs for the win imho.
There is also, of course, the issue of infrastructure dependence. Particularly since wireless telephony has moved almost exclusively to GNSS time we're going to have a really bad time if kessler syndrome takes out the GNSS satellites.
Edit: Here is an example adev chart for a inexpensive atomic clock vs what appears to be a pretty good timing GPS receiver: https://www.thinksrs.com/images/instr/prs10/PRS10diag2LG.gif
So in that case the GPS accuracy only beats out the free running atomic clock at intervals greater than 200,000 seconds or so.
Here is a collection of older timing receivers: http://www.leapsecond.com/pages/3gps/gps-adev-mdev.gif
A quick look didn't turn up any cheap non-timing receivers, but my experience is they're pretty bad (I mean relative to atomic standards, of course).
There are better timing receivers than the ones charted above, of course, but they are not $5. Their cost is now in the same general ballpark as surplus atomic clocks.
Of course, if you have both you can sync one to the other with whatever time constant maximizes the composite performance and have the best of both.
(and primary atomic clocks don't have this drift issue, but sadly the days of the occasional sub $1000 5071 showing up on auction sites seem to be over. :P )