I'm thinking of investing in SR VS seeker and FA Shaymin EX

These two cards, SR VS seeker and FA shaymin have been found to be staples for many decks. They can't be simply countered away from the format, shown by the wobbufett/garbodor/seismitoad/silent lab introductions to the meta, and seem to only go up in value

It turns out SR vs seeker is at its all time low of 17-18 dollars, and shaymin is around 30. With these cards always finding a place in the metagame, is it safe to invest 100 dollars or more in these cards? Their rarity also helps retain their value. They also aren't rotating at least for a year.

Not necessarily if you're looking to sell. I'd be inclined to believe you'd get burned if you stocked up on a ton of them. Plus, if you stocked up on a ton of them, you'd be driving the price up on yourself.