Your problem is what you are selling, and what it is priced at.

Shipping is not the problem.

You should set things up so that the customer pays shipping. When you start listing, your default settings are Free Shipping.

For something like this you can’t cut costs. You’re already at bare minimum. First class shipping is as cheap as it gets. Your cost for the item is what it is. Factor in Amazon fees. You’re not making anything. What you are doing wrong is pricing too low.

You pricing it wrong. Raise the price.

What you’re doing wrong is not factoring in your expenses when you set your price. The equation for profit is straightforward:
Selling cost - expenses = profit (or loss)

Your expenses include your cost to obtain the product in the first place (cost of goods sold), shipping expenses (shipping envelope or box, postage, bubble wrap, address label, tape), selling fees (Amazon’s percentage) and various other costs (utilities, costs of storage space, labor etc)

If you want to sell and make a profit, you have to ask yourself - if I price this at $X, and my expenses are $Y, what will my profit (or loss) be?

Apparently, you didn’t ask yourself this question. At $4, your expenses (approximated) would be -

• $1.50 Amazon selling fee
• $3.09 postage
• 25 cents for supplies (paper, tape, box or envelope)
• $1 cost to acquire goods

Total: $5.84

Then plug that into the profit equation:
Selling price ($4) - Expenses ($5.84) = Profit (or loss) of negative $1.84

Why not sell a 2 pack and add a foam brush and an instruction booklet? A nice “bundle” . Lots of added value right there and maybe an $11.95 selling price.