I would expect about 30% but it could be higher.
There is an easy way to determine the markup of any retail product sold anywhere. Just take a few moments with weekly flyers and do some simple math.
Grab the flyer, look for the sale price. Write down the original price and the sale price. Do this for whatever period of time seems appropriate. You want good data, so one or three examples is not good enough. There are reasons for selling products below cost, for example. So you want a dozen or two dozen inputs before you do your math.
Don't worry, the math is easy.
So, find the lowest sale price. Throw it away. Do the same for the highest sale price.
Add up the remaining prices; regular in one column and sale in the other.
So ...
4.00 ... 3.00
3.50 ... 2.96
3.75 ... 3.19
____________
11.25 ... 9.15
Divide the lower price by the higher. That's your margin.
9.15 divided by 11.25 = 0.81
The sale prices are 19% lower than the regular price (in this example). That's the Profit Margin.
Now, there is a difference depending on which way you are going. A discount is smaller than a markup. Consumers should be aware of this ... 10% off plus another 10% on is 99%, not 100% of the original price. Similarly, a series of discounts like 10% plus 10% plus 10% is 28% off, not 30% off.
Anyway, back to discovering our retail markups on anything sold by anyone anywhere.
Divide the big number by the smaller number (the opposite of your first calculator move).
11.25 divided by 9.15 = 1.234
The markup is 23.4%
You will find, when you ask someone who should know the answer, that your calculations are very close, if not right on, the actual numbers. The reason is retailers don't want to lose money but do want to rid themselves of inventory, so they offer items at a rock bottom price on sale.
The other issue that might rear it's head is seasonal variations. Certain products are closed out to reduce inventory at certain times of the year. You can account for that by continuing your little exercise once a month; you will see the period of the year when the usual pattern breaks and the lowest prices of the year arrive.
This is, by the way, very good information to have; it will save you huge amounts of money when you know whether to buy now or wait for the lower price later in the year.