When I helped painting houses (long time ago) I would get a third my partner received a third and whoever found the job received the remaining third. The customer paid for materials.
When you have pinestraw delivered and spread out you normally pay Cost of straw x 3. Materials = 33 1/3% and the rest is divided by the laborers.
Ideally setting a price on what you have made would go like this:
(Cost of materials plus time at a market wage) ÷ (1 - profit margin expected) = wholesale price
Most of the time there are middlemen type of agencies i.e. distributors, websites (your own or ones like ebay, pininterest etc...) that will add to the wholesale price.
(Wholesale price plus cost of warehousing, shipping, and distribution) ÷ (1 - profit margin expected) = retail price
This is how I would imagine selling a portable rocket stove kit that I might make:
(the materials may cost $300 + my time to assemble the kit - say 2 hours at $25) ÷ (1 - .50, profit % expected)
300+50 ÷ .5
350 ÷ .5
Now if I sell it to a retailer they are going to have to transport to their warehouse and send to each retail store. This cost will be added to the wholesale price.
At retail they will retail at 40% gross margin of if it cost $770 after the warehouse is done adding expenses.
770 ÷ .60 (1-.40) = 1283.34 and they will round it up to 1289 or 1299.
After labor, overhead, shrink, markdowns, marketing and other expenses the store may make 20% of sales. Grocery stores do really well to make 3.5%
Now for the kicker, will they be able to sell the rocket stove kit for 1299?
An example much closer to home:
My mother in law, age 84, started to make outfits to fit American Girl size dolls. She use materials that she already had and spent maybe 3 hours on each. She made a fabulous wedding dress as a special order. 6 dresses were made two years ago and were displayed on pininterest, ebay and in a local consignment shop. All the dresses were top quality but competed with poorly made imports. We started with $29.95 but have cut that price to 12.99. Today the second was sold for 12.99. She did not even get the national minimum for her time and nothing towards replacing materials.
So price has to also factor in what market will pay (demand). By the way, she enjoyed making the dresses and while she does not understand why they don't sell she is glad to have made them.
Selling something at a lower price to sell more will empty your savings real quick. Retailers lower their prices to sell more when vendors lower costs.
Holiday items start at full pricing then are promoted even marked down as the season dwindles.
So if you are selling something you made or a perform a service - investigate what other are charging and only make what you can profit from.
Try working the formula starting with the average market price is and work backwards.
Lastly, if you can sell because of value rather than price then you will profit more and customers will cherish your product.