I have a friend trying to put together a decent setup for his upright acoustic bass. Does anybody have any mic recommendations? I think he is using a fairly inexpensive dynamic and wants to improve that part of the chain.

Just to be clear - I´m no expert on the subject, I just bang my guitars & shout a lot + we play some kind of rockabilly I guess.
Our bassplayer uses this system http://kksound.com/products/bassmasterrb.php , previous to that he used a Shadow-mic, I think it´s this one : https://shadowelectronics.com/collections/upright-bass-pickups/products/sh-951 which sounds fine, but the K&K-system gives you more options: fretboard/neck and bridge pickups & separate 3 band eq for both inside the preamp-box + it can be louder than the Shadow pickup.
There are other makers off course from David Gage, Schaller, Fishman and probably a lot of other makers.
 
If it´s for studio use Dave Darling´s answers here might be useful: https://www.gearslutz.com/board/remote-possibilities-acoustic-music-location-recording/101772-recording-upright-bass-rockabilly-hints-tricks.html

I like using drum Mics for stand up double bass. Slaps can be loud. Double the volume of the bass. Ribbons are great.

Thanks guys.  Great suggestions. That kksound stuff looks like it might be really cool for him.  I sent him the link for their site, and someone else responded with the same info.  (He had asked on FaceBook.)

Most professional bassists I know will use a DPA 4099 for live recording or reinforcement.  Great mics with a dynamic, clean sound.  A couple years ago I recorded a Bass solo CD using a pair of Neumann TLM 107's for the Bass's spots, that worked out really well. 

Thanks.  The DPA was one of the first I found when I Googled and I told him that one as well.  I think he had so many friends respond with suggestions that the only problem he'll have now is deciding which one to choose.

AKG 414 ULS
 
on a budget, RE20, senn 441 or 421 all work very well
 
small-diaphragm mics are your best bet...
Neumann KM184
AKG C 451 B
 
ribbons can work too,
if you have a quiet preamp

personal taste, of course!
For pickups I like the K&K, just put their trio in my Santa Cruz dread and it sounds great. I seldom plug it in, so I wanted to keep it simple. K&K just seems to "get it" when it comes to simple pickups. I've not tried any of the other bass pickup systems, so I could be all wet.

For microphones, it depends on the musical setting, but mostly I use an RE-20, an MD-421, or lately a Royer R-101. I've also used a Fostex M88RP, a bit of an oddball, and it doesn't like every acoustic bass, but when it works it is pretty darned cool. If I had the budget I'd probably try a couple of the RCA clones, but I don't have the budget, so that's just an idea.

I've tried the AKG 414EB and C12A, and they were both a little too aggressive for my tastes. I've tried using one of them and a Royer R-101 and that was an interesting combination, very flexible at mixdown time. I've also tried both the Neumann TLM-193 (which works on almost anything) and a Shure KSM-32, but never found a sweet spot for either.

You can get a used RE-20 or MD-421 for a reasonable price on the usual auction sites, and that's where I'd start.