Calculating the sale price is as follows:
Cost of materials - how much the did the yarn cost you?
Cost of labour - how long did it take you to make? (Hours x rate = labour costs) for example: 8 hours x $10 per hour = $80
Depending on your level of experience, you can increase your labour costs accordingly.
Then you add your profit margin (this is actually how much money you receive after deducting all your expenses. You can include this as a percentage (10%) or a flat $ amount ($10).
Therefore,
Material costs + labour costs + profit = sell price
For example: $10 + $80 + $10 = $100.00