Depends on how your plan is set up. I have the very smallest text package (which I only have because my husband insists on me having it, I think we might as well push that money down the garbage disposal), so texts within my limit are a nickel or a dime each. Other packages cost a lot less per text. Texts over the limit are something like a quarter each.
Our talk time, otoh, is about $.10/minute from 7am-7pm M-F and totally free the rest of the time. So for the majority of the time, it’s cheaper for me if you just hold the phone to your ear and tell me, already.
As for the etiquette thing, if it’s actual useful information that is easier to read than listen to and write down, go ahead. But if you just want to natter about nothing in particular, call if you know me well enough to call and chat. But if you don’t know me well enough to call and chat, don’t waste both our time and money texting me trivial crap.