We're in the same boat (about to build a house, not sitting on $300K). We were about to start our build early last year but stopped before breaking ground when COVID hit. Well, the price of our house has now increased $150K in that time. Hindsight 20/20 and all that shit. We still haven't pulled the trigger due to uncertainty in the airline industry and sky high construction costs. Even though construction costs are insane, I'm afraid even if they do go down a bit, the interest rates will increase making it all a wash. A part of me just wants to say fuck it and pull the trigger and hope for the best.
To answer the OP's question, shop credit union checking and savings account promotions. Our SWA credit union offers 3% (it was 4% before COVID) on checking account balances up to $25,000 if you make 1 deposit and 15 transactions ($5 min) per month. The only ass pain is having to make 15 $5 Amazon gift card purchases per account, per month.