You must set at least a price with PURCHASE purpose to get a displayed price

If you don't set a price, either type (default being mandatory), with PURCHASE purpose you will get this message in eCommerce or Order Manager cart
Could not find a valid price for the product with ID [.....], not adding to cart.

Here is attached a patch which solves this issue. But I wonder if it's worth it because it adds some overhead. Maybe a simple explanation on top of Edit Price screen (EditProductPrices) could be enough. Would then be
<< You need to set a least a Default Price of type Purchase for the price caluclation to work>>