Product images sizes more consistent

Thumbnails size can be changed in the config under the tab files. You will have to delete the thumbnails folder under the upload folder so that new thumbnails are automatically recreated with the new size when they are needed.
CSS for all the front end pieces can be edited by clicking on the edit button next to the front end CSS option under the tab display in the config.
If you need different thumbnail sizes between the listing and the product page, you will have to edit the views where we display the images. You can find both by search for "product" and filter to display only the front end. You will have the show.php file and the listing_img{x}, {x} depending of the type of item layout you're using for the product listing modules.
You will have the $this->image object to which you will be able to apply different values to those variables before the call to the display function :

		$this->image->thumbnail_x
		$this->image->thumbnail_y
		$this->image->main_thumbnail_x
		$this->image->main_thumbnail_y

You have the "upload folder" option which indicates the path of the folder where images are stored under the tab files of the configuration. You can use an FTP client to access that folder and in that folder, you will see the thumbnails folder.

There is no relation between the thumbnails and the prices of items. Are you sure you didn't change something else ?

Do you have variants for the product ? If so, does the variants have a price ?