A dollar saved is worth 2 earned.
1. Make the call. Paint companies have reps. Some are hungry for your business. Compare prices annually and negotiate more favourable terms. Make it an annual thing - blame the calendar ("I'm making my annual call to all my suppliers to review my pricing for 2016"). Some companies will go as far as they need to in order to win your business. If you buy a decent amount of paint, you will have some leverage. Of course, price should not be your only concern when choosing a supplier. And everyone needs to make a living. A good supplier is like an ally to your business. A good price is important to your bottom line, but so is service, knowledge, stock levels, amount of locations, product range, quality, and so on. Weigh out all the factors, but don't assume you are currently getting the best price you may qualify for. Don't overpay for loyalty and convenience. If you buy $10,000/year in paint and can negotiate 5% savings, that is $500!
2. Consider switching to a lower quality line. With all the advancements in paint technology, you may not need to pay $40+/gallon for zero VOC, good quality paint. Shop around and learn about the latest offerings available. A newer, cheaper paint might preform better than your older, more expensive 'premium' paint. If you buy 2 gallons per day, saving $5/gallon might add up to $2400!...