'Parecer' functions just like 'gustar.' It also requires the use of IndirectObjectPronouns.
Las cebollas nos parecen baratas.
The onions seem cheap to us.
¿Qué te parece el costo de los zapatos?
What do youthink about the cost of the shoes?
¿Te parece caro el precio?
Does the cost seem expensive?
Costar
to cost (Impersonal....'ish' verb)
¿Cuánto cuesta la cebolla?
How much does the onion cost?
¿Cuánto cuestan las cebollas?
How much do the onions cost?
This verb can only be used to tell the cost of objects since only objects have cost. However, it is NOT a true impersonal verb since it does not require IOP.