We are working on making this more clear. Basically some products have options and the collection page is showing the price of the cheapest one, while on the product page the option selected might be a different one. For example there is a standard T-shirt for $30 and a rainbow one for $35 (it costs us more to make those) so in this case the default product price will be shown as $30 and change to $35 when the rainbow option is selected.