I don't know if this is helpful or not. But when I used to produce DVD's of dance recitals, I charged nothing for the production services. I just required them to buy a minimum number of DVD's. For a really simple dance recital, I wholesaled to the studio at a low disc price so they could add profit margin and still sell the DVD's for less than $19.95 (remember you only charge taxes when you sell to the consumer, so let the company deal with that problem.) Rather than trying to sell the DVD's as cheaply as possible, I wanted them to cost what is typical in the marketplace. So I charged $17 per disc. My clients were not surprised at the price, only that I'd do the production for "free."
Charging the same $17 per disc, you'd earn $1700 dollars. And every disc after that would be pure profit. Actually worth your time to duplicate just a few DVD's. Don't be fooled into thinking a low price per disc will encourage sales. If it priced dramatically below market, your clients will think it is an inferior product. So don't even consider selling for less that $10 or $12. They just won't take you seriously. And most clients can't tell an adequate job from an excellent job, so they judge the quality by the price. And don't you want them thinking your work is a cheap knock off.
When you are calculating your costs, give yourself a salary for the 20 to 25 hours the duplication will take.  And don't forget that the ink for printing will cost more than the disc (assuming you put a color background or graphics on it.) And I feel i would be remiss if I didn't mention outsourcing your duplication. They have a do-it-yourself custom service where you send in the duplication master and they return your initial 100 in just a few days, then you can have them duplicate DVD's anytime later using a free "storefront" online. They charge like $10 a disc for the service, so you'd want to bill for your production expenses. Then you can add your profit margin to the DVD's and whenever you sell thrm, they take care of duplication & shipping and send you a check. I know several companies do this, but I'd choose Disc Makers for personal reasons.
Sorry I prattled on for a bit. But trying to get the lowest price for your DVD's is a lose/lose situation. You lose out on money they expect to pay and they view your work as a discount production. So they won't think of you for their big deal productions. The theory behind this is found in marketing research. Consumers will buy an inferior but more expensive product because they believe expensive is better (in general.) Since DVD's from a store cost around $20, significantly lower prices will represent lower quality to the consumer.
