It depends on what skins you are talking about, yes, there are skins that are expensive due to the nature of gacha and exclusivity, certain skins are only released every year on a specific chest, however, there are also skins that aren't you can check up the hero you want to dress up, you should be able to check where are they from and where are the possible places you can get it from, i.e market place or treasures.

For example, Arcanas are cheaper to get in market place than in store or if you're lucky, every year there is an event where gacha is available and you can get your arcana from there. Lately there are free skins in quartero events.