How much is kelp?

Excuse me, could you possibly enlighten me on the matter of kelp pricing? I've been curious as to how much kelp actually costs. Is it priced by weight, or perhaps by length? Does the type of kelp, such as brown or green, affect the price? Also, does the season have any impact on the cost of kelp? I've noticed that prices of produce often fluctuate depending on the time of year. Would you mind shedding some light on this topic for me? It would greatly assist me in making a purchasing decision. Thank you for your time and assistance.