I looked it up. Some better known members of the Mysterious Gensokyo cast:
Satomi Satō (Reimu, Letty, Yuyuko)
Yōko Hisaka (Marisa, Mokou, Eiki)
Madoka Yonezawa (Sanae, Patchouli)
Yui Sakakibara (Yukari, Tenshi, Komachi)
Omi Minami (Suwako, Meiling, Youmu)
Yukana (Kanako, Cirno, Hijiri)
Kaoru Mizuhashi (Sakuya, Nitori, Kasen)
Mariya Ise (Flandre, Utsuko)
Source:
a comprehensive list of voice actors in Touhou fan worksAs far as I know, the seiyuu industry's rules are: young seiyuu are always poorly paid - if they become popular, it just means the industry can exploit more from them; the only seiyuu who are well paid are veterans who have stayed at the top of the industry for a long time. Not very different from Japanese showbiz in general.
The Koumajou Densetsu cast has some bigger names. On the other hand, Mysterious Gensokyo has a larger cast. I don't know enough to say which is more expensive, but Aqua Style might be able to save more costs since they reuse their assets over the expansion packs and updated versions.