I played string bass in jazz bands in college (unplugged and pizz), but since then I've played almost exclusively electric. So, of course, my calluses are gone. I still have my string bass, but I can't pluck it hard enough to get a decent sound even on the Thomastik "weich" strings while avoiding the blisters.

I want to use the bass for some recording, so acoustic volume is not too important.

The student basses at Sam Ash all seem to be strung with light gauge roundwound strings that have a fairly thin tone but sustain very nicely when played pizz.

Can anyone suggest some string makes/models of this type that I should consider? And low-price sources for 'em?

While I can't be too much help on which strings to buy, I did want to recommend lemurmusic.com as a source for inexpensive strings.
I haven't actually checked them myself but I did browse through their catalogue and they seemed to have pretty inexpensive prices for the items that they are selling.
I hope this helps in some way.

I think some people have recommended Corellis as very light guage strings for the double bass. Why not do a search on these strings in this forum?

Obligatos would be a string friendly to Slabb-y fingers :)

Also -- the only way to get your callouses up and avoid blisters is -- to get your callouses up. This will go for any string, and you're not going to get much of a sound until you get some callouses and strength together. Getting a softer string just for the purpose of getting a sound with no chops won't fix your problem. Just put some time in daily and you'll start getting your callouses together pretty fast.

I've been playing for twenty years now, and I still pull my fingers raw by the end of a hard-playing, high-volume, sans-amp gig. I haven't had a real blister for years, but I will pull an air-pocket under the callouse sometimes. Kinda grody when the bubble surfaces -- big chunks fall off of your finger :Þ

Thanks for the suggestions. I did look a lot at the Lemur catalog, and almost bought some Corellis. But I wound up playing the session with the Thomastiks -- never did get new strings.