Backtesting

Start by getting historical data from yfinance and run it through some hypoticals using black scholes model. if it works there then spend some $ and get the full set of real historical data 

Alpha Vantage offers some of the best pricing out there, and they're willing to negotiate if you find a better deal elsewhere. Their API limits are generous too. I'd recommend reaching out as they offer solid one-year deals and a generous 15-day free trial.

Massive is probably the most robust option. super clean api and docs, but it’s also one of the most expensive.