I have problems seeing the cones in my small gas kiln. The flames play havoc with viewing the cones, especially in reduction. This stuff is harder than is seems it should be. I agree with Babs: hearing other's struggles validates my own.
$300 is a good starting point. Ask him when he last changed the elements and to what cone he fired the kiln. This will give you an idea of how long your used kiln elements will last. If they have been replaced in the last 3-4 years, it should be fine, especially he fired to 05-6 cones. If the kiln is an L&L, buy it.