The Collaborative International Dictionary of English v.0.48:

Unprosperous \Unprosperous\
   See prosperous.

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "unprosperous":
   badly off, broke, depressed, destitute, dire, distressed, donsie,
   doomful, down to bedrock, embarrassed, evil-starred, fatal,
   feeling the pinch, fortuneless, funest, hapless, hard up, ill off,
   ill-starred, impecunious, impoverished, in Queer Street,
   in adverse circumstances, in narrow circumstances,
   in reduced circumstances, in straitened circumstances,
   inauspicious, indigent, land-poor, low, luckless, narrow, needy,
   ominous, on the edge, out of luck, out of pocket, pinched,
   planet-struck, poor, poorly off, reduced, sad, short,
   short of cash, short of funds, short of luck, short of money,
   squeezed, star-crossed, straitened, strapped, unblessed,
   underprivileged, unfortunate, unhappy, unlucky, unmoneyed,
   unprovidential