Like most Pokmon cards, the value of Jolteon depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Skyridge)
I look for a little more in commanders, however
Iono is a lot like Marnie, but with even greater strategic potential
OP-13 offers something for every type of buyer but the right approach depends on what you are after
If you really want to go all in on restrictions, Urtet, Remanat of Memnarch and Avatar Aang are only going to get some beginning support from sets and maybe sporadic or never again support
Pokmon Original Partner cards: Release date and what to expect from the 30th anniversary set We all start somewhere