Stats:

Difficulty: https://www.bitrawr.com/difficulty-estimator https://www.coinwarz.com/mining/bitcoin/difficulty-chart https://bitcoinexplorer.org/difficulty-history https://insights.braiins.com/en/cost-to-mine/

Hashrate: https://www.coinwarz.com/mining/bitcoin/hashrate-chart https://bitinfocharts.com/comparison/hashrate-btc-ema14.html#3y

ASIC Prices: https://data.hashrateindex.com/rig-index-data

A great tool to monitor the progress over the 2,016 block epoch is fork.lol's Difficulty Retarget chart: https://fork.lol/pow/retarget

And a great Dashboard, overall: https://timechainstats.com