So what my logic has been is to bid graded cards based on their PSA graded value plus a few extra dollars that would allow for the cost of grading.
A card graded as NM-7 (lowest grade I will pick up, generally) with a value of $8 would be a negative $7 since the cost to grade the NM 7 is $15. Math has never been my strong suit but I know that $15-$8 = loss of $7.
As an example I purchased the following PSA Graded 1963 Topps; #49 Dal Maxvill graded a 7 NM for $10.50 and the card is valued at $8-so "loss" of $2.50.
#336 Ed Bauta also a 7 which I won for $8.50 and PSA says I paid 50 cents more than its value.
Last but not least, #533 Bobby Shantz Graded an 8 (NM-MT) for $9.54. This card is valued at $22, so a gain of $12.
So why would I pay $15 to grade any of these? The answer is I wouldn't. There are some heavy hitter Redbirds I need and these I will pick up nice graded copies but I am not sending the others in just yet.