Buying a hard drive, a stack of RAM or a LiFePO4 battery? The sticker price tells you little: a 20 TB drive for $260 is a better deal than a 4 TB drive for $70. PerUnitPrice does the math for you.

It pulls new and used listings from eBay several times a day and ranks them by price per unit: $/TB for HDDs and SSDs, $/GB for memory and GPU VRAM, $/core for server CPUs and servers, $/port for 10GbE gear, $/kWh for LiFePO4 batteries and power stations, $/W for solar panels and $/kg for 3D-printer filament.

Filter by capacity, interface, brand, socket or voltage and jump straight to the cheapest listing per unit. Free, no sign-up.