There are a few direct trains, but if a site is giving you quotes in US$ and/or using AM/PM times, you are on a reseller site. Always check the actual Trenitalia site to be sure.
There is an IC train that departs Pisa Centrale at 13:42 (1:42 PM) and arrives to Monterosso at 14:53 (2:53 PM).
There is a return IC train that departs Monterosso at 17:07 (5:07 PM) and arrives to Livorno Centrale at 18:42 (6:42 PM).
That gives you about three and a half hours in Monterosso, maybe enough time to see one other village. Note that the IC trains do not stop in any other CT village, so you'd need to get back to Monterosso to return (or to La Spezia, where you could also pick up this train).
The fare will vary based on when purchased, these seat-assigned trains use dynamic pricing.
Source material here: EN - Trenitalia