I'm a new racquetball player, playing once or twice a week. I'm not a power player nor do I play with many people who are. I noticed that balls sell in bulk for less than $1 each and was wondering if that would be an easy way to ensure a supply. However, it may take many months (a year even?) to go through them all. Should I be concerned about deterioration once the canister is unsealed?
I'm a tennis player, but a similar principle applies with racquetballs.
For tennis tournaments in the league I play in, each player is required to bring two sealed cans of three tennis balls, one can for warm-up and one can for tournament play.
Sealed is important because pressure inside tennis balls are inflated to about 12 psi greater than normal air pressure. Sealed cans ensure the tennis balls are "housed" in pressure equitable to internal tennis ball pressure.
Once the can is unsealed, the "freshness," as you put it, slowly fades. This is the best time to use tennis balls so the pressure inside the tennis ball is closest to its inflated pressure. This results in the bounce being consistent, reliable, and optimal.
Any "deterioration" will come from normal air pressure, causing the ball to be less consistent, reliable, and optimal...and will eventually go flat. This difference is marginal to the casual/recreational eye, but significant to the competitive eye.
By the sounds of it, you will have an adequate supply of racquetballs if you decide to use them the way you intend to as stated in your question.
Yes, unless racquetballs are in sealed, unopened, canisters, then all of the balls you buy will go flat together over time - especially if it will take you a year to go through them.
While racquetball ball freshness is important in competitive play, as a new player learning how to play, ball freshness is much less critical. If you play with a variety of players or there are a lot of players at your club, you'll likely also find that balls get swapped around frequently.
If you can afford to use new balls often, then it is optimal to always have a fresh, unopened can handy, but you can usually get quite a bit of play out of a ball while you're learning.
A good rule of thumb when comparing balls is to hold two balls in your hand and drop them at the same time. Play with which ever bounces higher.
For anyone interested, the 2013 USAR rulebook describes the official characteristics of a racquetball as follows:
(a) The standard racquetball shall be 2 1/4 inches in diameter; weigh approximately 1.4 ounces; have a hardness of 55-60 inches durometer; and bounce 68-72 inches from a 100-inch drop at a temperature of 70-74 degrees Fahrenheit.