I usually just let cash accumulate and buy on dips. I buy bigger chunks and eat the commissions, which are pretty low in any case. Alternatively, I suppose you could get one of those Wells accounts that has 100 free trades.
Try BuyandHold brokerage. $16 per month for unlimited trades (market orders only, three trading windows during the day). Free dividend reinvestment. Or $7 per month with two free trades.
https://www.buyandhold.com/