You can add your own prices, and if you add your own price that has the same "material" as the price provided by the vendor, then your price will become the active one and the vendor price will go away. For most items, from most vendors, that means adding a price that has no material (just leave material blank). Then add your retail price in the Cost field.
If there is no price rule in place, then that will become the selling price. If the brand has a price rule in place, then you will have to put in a COST price that marks up, using the price rule already in place, to be the retail price you want to use. Of course, if you are changing a bunch of prices that have a price rule, you could just change the rule too and have the same effect. keep in mind, though, that the price rule affects EVERY item from a brand, the whole brand.
To override vendor provided price with your own price:
From the Dashboard go to Catalog > Items
Click on the item you want to edit, then:
Click "Add another price"
Now you have both prices showing temporarily:
At the bottom of the page, click "Save and Continue Editing"
And now there is only ONE price, and it is YOUR price!
To remove your price, click on the red 'X" next to the price. Then click on "Remove"
Now you will have NO prices showing temporarily:
Again, click on "Save and Continue Editing"
Presto! The original vendor supplied price is back!
Pretty cool, huh?
One last thing to remember! When you add your own local price, make sure you check the "Default" checkbox all the way on the left of the price entry. That makes the price show first, and also show period, in list pages (pages where multiple items are shown at the same time).