A spray-in bed liner runs about $650 for a full-size pickup in most US shops, and spring is when you can usually talk that number down a little. Winter slows the install bays, so March through May is when shops are most willing to run promos, throw in UV protection, or knock off the tailgate if you ask. The product is mostly labor and a catalyzed coating, so shop overhead matters more than brand, which means you have room to negotiate.
Financing is where people get tripped up, so keep it separate from the price talk. A 0% purchase intro window is a tool for spreading out the deposit and the extras, not a reason to skip haggling on the total. Get the cash price down first, then decide how much of the bill you want to put on plastic and over how many months.
Honest catch: the 0% intro window is a deadline, not a discount. If a balance is still on the Citi Simplicity® card after 18 months from account opening, the standard APR kicks in on whatever is left and starts adding interest from that day, so set a payoff reminder a couple weeks early and clear it before the clock runs out.