Best way to test new flavors before a full product launch?

For 4 flavors on a budget, I'd skip traditional focus groups and go with an online concept + simulated taste test combo — you can recruit 150-200 targeted respondents through something like Respondent.io or even a Subreddit community for way less. If you can get samples into people's hands, a monadic sequential test works great to get clean preference scores per flavor. That'll give you statistically solid data to cut from 4 to 2 without the overhead of full focus group facilities.