If you get FoV, then you can install it, start the game, load your last save in the Hall of Echoes, finish off that fight and continue into FoV with the same character.
DKS includes the remastered D2:ED (redesigned flying fortresses, changes to enemy placement, changes to the loot and enchantment systems, etc) along with FoV, but unfortunately saves from the original D2:ED are not compatible. You could start a new level 35 character at the beginning of FoV, though (as you can with the original D2:ED and FoV installed).
If you are patient, DKS goes on sale occasionally on Steam, etc (Amazon just had it for US$8 on the weekend, but it is back up to regular price now). If you do decide to get FoV, after you finish with your current character, there is a large
conversion patch to turn D2:ED+FoV into DKS, so with your next character you would have the option of playing through the remastered D2:ED.
