I recently invested in the Rebel 3 starter kit with battery, tank and coil. Now I learn that if you buy from Vaporfi they got you by the balls because you cannot interchange product with other manufacturers. It's like they corner the market and trap you . Is $17.99 plus $3.95 shipping a fair price for a 5 pack of coils.? Does anyone know if another kind of coil would work in the Rebel 3 tank. Thanks.