What would be a fair price for a used, supposedly in excellent condition, 5.75" concentric coil for a Cibola? They run around $105 new. Also, for those who have one, are they worth the money over the standard coil? And one last one, which would you prefer, the 5.75" coil or the 12x10 (does the latter go that much deeper?) I relaize they are for different situations.