ê° = price, value. This is very broadly used word ranging from price of an item (ëŹŒê±Žê°) to a more abstract meaning like value (ê°ëê°ë€ = is valuable).
ê°êČ© = a (fixed) price of an item. This is the most common word for "price" in commerce. (ëŹŒê±Ž ê°êČš = price of an item, í ìž ê°êČ© (or í ìžë ê°êČ© = discounted price).
ëčì© = cost, expense. This usually means the expenses required to do something, like traveling to a place, setting up a business, etc. (ìŹí ëčì© = travel expenses, ìŹì
ëčì© = cost of business).
ê° and ê°êČ© have fair amount of overlap in usage, whereas ëčì© doesn't.