I thought about this a few months ago and decided that surveymonkey would be the best option given my overall diligence cost. From my experience in consulting, GLG/Guidepoint will be too expensive for the transaction costs we generally see here. Happy to talk offline. Thanks!

We recently solicited proposals from several vendors, and we received solid proposals from GLG, Guidepoint, and NewtonX. Each was eager for our business despite that fact that our target N is smaller than yours. All 3 of those vendors will source the respondents for you, host and administer the survey (pretty much all of them use Qualtrics), and provide you a raw Excel file with the outputs. In all 3 cases, their minimum engagement fee is $5k but yours would probably be a good bit higher given your target N = 500. I can't comment on the quality of their work because we are in a holding pattern with the target acquisition and we want to get closer to LOI stage before committing to the survey.