This is a million taco question! The value of a taco depends on each team and the strength of its Taco Economy. This is why we recommend waiting to add rewards until after a few months of using HeyTaco. Waiting to add rewards allows HeyTaco admins to see how many redeemable tacos people have accumulated and how engaged your team is, which allows you to price rewards accordingly.
For custom rewards, we always recommend pricing them higher to start with and then reducing the price if it takes people too long to redeem a reward. By higher, we recommend a starting price of 4 to 5 tacos per $1 a reward is worth. For example, if you want to have a T-shirt reward that costs you $10, we recommend it having be worth either 40 or 50 tacos.
For collaborative rewards, pricing depends on how many people you expect to contribute to the reward. We recommend the following formula for pricing team rewards: 30 tacos multiplied by number of people you expect to contribute to the reward (for example, 30 x 8 people = 240 tacos).
A common thing that happens is for a team to use HeyTaco for a while without rewards, and then deciding to launch rewards after some time. What that means is that people on the team have accumulated lots of redeemable tacos and will be able to deplete your rewards supply within hours. If that is the case, we recommend resetting everyone's Redeemable Taco balance and starting from scratch. Resetting redeemable tacos will only affect the taco balance people can use for rewards, and will keep the tacos given and received balance intact, ie your Leaderboard will stay the same. By resetting redeemable tacos, you are resetting your Taco Economy and people will need to earn their redeemable tacos anew. This allows you to price rewards more reasonably (see guidance above) and avoid taco inflation (it is a thing, even in the Taco Economy).