Minimum is 250, that's true. You can only add higher prices. If you want to add higher price than what is said in recommended price, then uncheck the recommended price, check the $ box and type in your new price.
Another way is to go to Your Online Files and behind each image, click on the edit button.
If pictures are under review, then you cannot edit any info. Wait. Once the image is accepted, you can modify info.
You should also know that the recommended price or the price you type in into the box is the price that the buyer pays. You will receive 50-60% (depending if you are exclusive or not) of that price (if recommended or your price is 500, then you will receive 250...300).