Temporary root concealers (sprays and powders) and permanent at-home kits both cover gray regrowth, but they solve different problems at different price points. Whether one is cheaper than the other depends entirely on how often you use the concealer and whether you still get salon touch-ups on top.
What each product does
A permanent root touch-up kit, like Madison Reed Root Perfection (~$38, 2 applications) or dpHUE (~$37, 2 applications), deposits permanent dye that bonds to the hair shaft. Coverage lasts 3-6 weeks and survives washing. One touch-up costs about $18.50-$19.
A temporary concealer like L'Oreal Magic Root Cover Up (~$12.49 per can, about 30 uses) or Garnier Express Retouch (~$12.95) is a cosmetic coating that washes out in the next shampoo. It is not dye. It buys you a day or a weekend, not weeks of coverage. Cost per use is roughly $0.42-$0.43.
Annual cost comparison
At a 4-week cadence (13 touch-ups per year), a permanent kit runs about $247 per year (using Madison Reed at about $19 per application). That is your complete cost if you are fully replacing salon visits.
A temporary concealer used twice a week year-round costs about $45 a year, roughly 104 uses at $0.43 each, or about three to four $12-$13 cans. The catch is that most people reach for a concealer between permanent touch-ups or salon visits, not instead of them. If you still pay salon prices and add $45 of concealer on top, the concealer has not saved you anything. It has added to the bill. To cut your yearly cost you have to replace the salon, which is what a permanent kit does; see the Madison Reed vs salon breakdown.
When a concealer makes sense
Concealers are the right tool when you have a few days left before a scheduled touch-up and your roots are showing at the part. They are also useful for spot coverage at the hairline for photos or events. At $12-$13 per can with roughly 30 uses, they are cheap on a per-use basis.
They are not a cost-effective replacement for dye if your goal is continuous gray coverage. A single can lasts about 15 weeks at two uses per week, so year-round use is roughly three to four cans, about $45. That is cheap, but the coverage washes out every shampoo, so you are not covering your grays the rest of the time.
The cheapest overall approach
The lowest annual cost for consistent gray coverage is an at-home permanent kit used on a 4-6 week schedule, with a temporary concealer kept on hand for the last few days before your next touch-up. At roughly $247 per year for the permanent kit plus $20-$30 in concealer, your total stays well under $300 per year.
Compare that to salon touch-ups at $1,200-$1,800 a year before tip, and the permanent-kit-plus-concealer combination saves most people $900-$1,500 a year. Run the gray root touch-up calculator with your own frequency and salon price for a number specific to you, then see how to stretch the time between visits to push it lower.