Do the math, take the list price of the kit and deduct 30%-40% off to get the LHS cost. Typically a LHS doesn't sell for list prices (though some do) they typically mark the price down 10%-20% to be competitive.
Example:
MSRP Kit: $36.00
Dealer Cost $21.60 40% OFF List
Dealer Selling Price $28.80 ($29.00) 20% OFF List
Net to LHS $7.20 or equal to about an hour of one employee's time.
MSRP Paint: $3.99
Dealer Cost $2.39
No Discount on Selling Price.
Net to LHS $1.60 The store would have to sell 5 bottles of paint to match that of what the kit equaled in labor.
The variable in your question is what are the prices of the items you purchased. The greatest profitability isn't the kits, but the consumables such as paints and cements, items that need to be replaced frequently by consumers as they use them. When a store sells an item and restocks it, it is called a turn. The more turns a product produces the more profitable it is. Store owners need to have products that turn at a minimum of 3x (fair) but 6x or more (is excellent.) This is generally a per year bases. As a hobby shop manager I like to see the paint racks need refilling monthly, with the most popular colors refilling each week.
Sure there will be orders that only have one item, but they are offset by those with multiply items...the goal is to have lots of orders not just a couple per day/week/month or well if it reaches beyond a month things are likely terminal.