All due respect, there is on point that your are missing in that calculation which is Cost of Good Sold (COGS). In your first calculation if your conversion rate is 1% and sell the product for $50 and even products cost is $1, you are losing $1 in every sale if the cost of the product is $20 you lose $20… So you may add COGS to your equation in order to be more accurate.
(SP-Pr-COGS) * CR
And it perfectly illustrates why the Conversion Rate (largely influenced by the copy) is such a critical factor to success.
Joshua Aaron Stanley
Internet Sales Copywriter