Hextech Rerolls

Maybe its just me, but I never get any good rerolls. Just now, I rerolled a bbq Leona permanent shard, darkrider sejuani shard and gentleman chogath shard, those are 750, 975 and 1820 rp skins. I chose to reroll because I didn't own any of those champions and it gave me 100 essence along with Uncle ryze, which costs 520rp. Shouldn't there be some sort of rule in place where at the very least, rerolls won't give you a skin worth less than the lowest priced skin shard in the reroll? It just doesn't feel very fair.