For the budget you are proposing, an AGA 20 xh would work for seahorses, they fit the footprint of a 10 g and they are 24"tall. An Eclipse 1 hood fits on for filtration.
I know very little about jellies, but for anemones, you'd want some decent lighting, and for the size of tank that you'd need to accomodate anemones and their lighting, you'd probably be over budget.
All of the things you are proposing are very specialized. I'd recommend
Joyce Wilkerson's Clownfishes and Host Anemones book or Frank Indiviglio's book on Seahorses, as well as Tracy Warland's book on seahorses.
HTH
Jenn
__________________
Member of the "J" Crowd & the BRW Crowd!
LFS Owner:
Imagine Ocean

Just keep skimming, just keep skimming, just keep skimming, skimming skimming! What do we do? We skim, skim, skim!