How to market mvp before narrowing down specific niche?

First time founder, long time dev here.

I’m working on an easy to use event calendar builder that allows small business owners to embed events on their sites (ie: gyms, bars, etc). Think Carrd but for event calendars.

The plan is to cast a wide net, and charge a low price then build out offerings into whatever industry gains the most traction.

Does anyone have any specific marketing recommendations for reaching a non-focused audience? Since the product will be cheap/ freemium I can’t really rationalize too many paid ads.

My thoughts are:

1. Tweeting/ contacting Carrd users who would want to embed an event calendar.
2. Reaching out to agencies who create the sites for these small businesses
3. Straight up cold emailing sites with hideous calendars

Thanks for the insights!