I got in the 1400's while fighting a Desert Siren, those have unlimited health, I think. I used the Dairy *******, secret costume unlocked by beating Challenge of the Gods. It has UNLIMITED MAGIC, so instead of ripping the head off the Siren I just tried something else... This is no lie, its all true. Works on Medusa, too, although you will only have lvl 1 Poseidon's Rage by then.
It's been a while, hasn't it?