I'd recommend AudioScienceReview for anyone looking for measurements-based evaluations of audio equipment instead of the weird and wrongly incentivized audio review ecosystem.
A cheap pair of Sennheiser HD600 for headphones will last effectively forever and sound great paired with a very competitively priced Topping DX3Pro+ for external soundcard/amplifier.
It's really hard to estimate the amount of time. Even spending 40hr on it wouldn't be worth it from a purely financial perspective even if you ignore ads and other costs, and I spent many times that in terms of time.
But at the same time, doing this helped me reach over $6k MRR this year. Could I have gotten out of the tar pit faster? Definitely.
For https://poach.vc/ and https://data.poach.vc/ I just emailed and LinkedIn DM-ed a ton of people. Since the newsletter features founders and investors, I also tag them each issue on Twitter, which is a small but evergreen source of exposure.