I think that the best way to do that is to think on percentages rather than in cents or dollars. As you said, fees are important if you make many little purchases, but if you buy less often or higher amounts at once, fees get diluted.
Capital availability decides your repeat purchasing time too. Like if you can have only $10 weekly for investment, you will need to wait like 5 weeks or 10 weeks to do each DCA round with either $50 or $100 purchase. It will save your trading fees, and your withdrawal fee too.
People with big capital don't have to care too much about withdrawal fee or on chain transaction fee when moving their bitcoin. Because withdrawal fee or transaction fee is surely too small compares to their capital value or withdrawal value.
Anyway, if you will lose a great opportunity to buy just before the FOMO like what we are seeing these days, then perhaps you should forget about high fees and buy before it gets more expensive.
Buy in a bear market, especially 1 or 2 years since ATH of last market cycle, is very good for accumulation, reduce risks of buying in middle of correction from ATH to bottom, and it reduces your entry cost so that in a next bull market, you will have better ROI.
During a bull run, simply do DCA if they have capital for it, and if you want to invest more.