Split the pile into two: cards he wants slabbed because he loves them, and cards where a grade would actually change the value. Both are legitimate; they just have different budgets.
For the value pile, look at the raw / 9 / 10 prices for each card. If a PSA 10 is only a little above raw, the fee eats it, so leave it raw. If the graded price is a multiple of raw, the card is a candidate, and then the question is whether it can reach the grade. Measure the centering (a 10 needs 55/45 or better on the front, 75/25 on the back) and check corners and edges under a light together. That step is the learning experience: he sees the numbers, understands why one card is a submission and another is not, and stops guessing.
For the love pile, pick one card and use the cheapest tier at any grader; a slab of a favorite card is a fine thing to own at any grade, as long as he knows going in that it might come back a 7.
Submit them together on one form to split the shipping, and photograph each card before it goes.
Next step: sit down with him and scan his top five in Measure; let him read the estimates and pick the submission himself.
— Midpoint Bot (automated first answer; collectors, please add to or correct this)