My friend planted three rows of basil in his garden to make pesto, and now we need to source roughly 25-50lbs of parmesan. With that kind of quantity, cheaper is better.
The price of genuine-sealed-and-certified parmagiano reggiano is quite high and fairly consistent, especially for more aged varieties. I think your best bet to save money will be to use a similar parmagiano reggiano cousin, such as grana padano, romano, or a quality Argentinian reggianito. As a second-tier approach, you might look at domestic Parmesan, but use caution as it may not have the same quality as a one of the Italian imports.
As for genuine Parmesan: you're buying at least a couple hundred dollars of cheese, and this gives you some bargaining power. Buy or ask to taste a small sample of whatever you're considering, and try to negotiate; managers may be willing to offer you a bulk discount. I'd gather a couple quotes from cheese shops, try prices at your local Costco/Sam's Club, and talk to the upscale grocery stores in your area.
As far as pricing goes, I've seen genuine-seal-and-everything Parmagiano Reggiano on sale at about $12-13/lbs at my local Southern Season. I generally expect to pay $18-22/lbs at upscale grocery stores for Parmesan, with remarkably little variation between stores. Your standard grocery stores tend to sell small blocks of inferior-quality and freshness Parmesan for similar prices.
In contrast, grana padano runs around $12-13/lbs on average at my local Trader Joe's, and might be available for under $10/lbs with a good sale. I usually buy blocks of that for general cooking use, as it is close enough in taste and much cheaper.
Costco has good quality, large chunks of parmesan for a lot cheaper than grocery stores.
Well, it's not first frost yet in most areas, so you might still have time on this --
I'd ask your local Italian restaurants where they get their cheese from. Odds are, they're not paying the grocery store $15-20/lb prices.
In my area, there's Restaurant Depot, which sells Parmagiano Reggiano cheaper than some of the regular grocery stores sell other cheaper varieties. The thing is, they sell it in chunks about 1/8 of a wheel or larger if I recall correctly (which is about 10lb a chunk ... maybe they had 5lb chunks, but I don't think it was smaller than that), and they'll only give membership cards to people who can prove they have a business or a non-profit ... but it's possible that a restaurant who already has a good source might be willing to resell some to you.
We find good values at our local ethnic market -- specifically, in my case, Phonecia Specialty Foods in Houston, TX. They have no problems selling in bulk by the wheel.
This is just plain silly! You can get grated domestic parmesan at ca 4.14/lb in bulk foods section of WINCO supermarkets. Plenty of flavor, particularly if making pesto