i bought one from the Millionaire Center, but there's none in User Shops. what's it worth in SP and CSC?

No more than Millionaire Center price until it retires (if it retires) [edit] And that comes out to ~35 CSC

so what's that in SP?

never mind.

1.75m, same as the MC price. At a maximum; you might not be able to get that for it since anyone could just go to the MC and buy their own.

The Millionaire Center used to be time-limited, so nobody could go there more than once in any twelve hours. Because of this, there was a (light) demand for MC items, in that someone would be paying a not-too-extra extra cost you were charging, to "buy your turn" from you. Magical Keepsake Boxes were also deprecated, so there's no sP to be made on bulk sales of these either.

Nowadays the MC is made a more ferocious sP-sink, and a round of quests'll get anyone the price many MC items, so there's just no reason to restock from there unless you're going for the Achievement. All Achievements have some cost either in time or skill or sP. Since the time-limit was removed, the only way to get these is MC ones is at a loss or with a lot of good wealthy friends who don't care about getting them themselves, sorry.

It used to be possible to make a "save you the schematic creation time" profit available in Purveyors of Plans in Atebus, but either enough folks are making mistakes or just have it in their head that nobody's time sjworth scrip so it is not easily possible anymore.