Plans from the major carriers are insane, the price structure is always like $80 for the first line plus $10 per additional line, so unless you have four phones on your plan you're really getting screwed.
In comparison, Mint's plans are $15 to $30 per line if you prepay for a year at a time, and there's no extra activation fees. It's been working well for me.
If your phone has eSIM support you can probably install their app and run a free week trial alongside your current phone service if you want to test it out. For older phones they sell a $5 test kit with two SIMs, one for the trial and a second to activate a real account, and it includes a $5 discount to pay back the trial cost.