Most of the cost associated with research is actually the cost of accessing a sample, so if you can figure out that piece, you should be in a much better spot. A couple of ideas:
1/ Talk to your happiest, unhappiest customers, customers that churned, and "prospects", if possible. Use your budget for incentives. This sample will at least give you the "extremes" of attitudes.
2/ There are some helpful online tools that you can sign up for and "trial" them at no cost- Optimal Sort, UserTesting, SurveyMoney, GetFeedback all have some sort of free trial. You can even take respondents through design files on something like Figma if you're looking for product feedback.
3/ Figure out beforehand what you need for "significance". Some organizations really do need the quantitative, large sample required to get to statistically significant answers, but if you're looking for a "gut check", you'll be fine with a small (n= 30) sample!