Call up a few prospects, explain to them your value proposition, then ask them "how much would you pay for this?". Get the average of those prices. Then call up

Call up a few prospects, explain to them your value proposition, then ask them "how much would you pay for this?". Get the average of those prices. Then call up a few more, explain the value proposition again, but this time tell them directly "Would you pay X for this?". If they seem okay with it, that's a good price to start with (you'll most likely go up since people usually accept a higher price than they think). If that price isn't what you're hoping, then iterate on how you communicate your value proposition.