Most injection systems are rated for 20% bio aka b20 without voiding the warrantee. Bio beyond that doesn't have enough lubrication so you have to supplement it with a splash of something like 2-stroke oil. It can run for a long time like that without hurting the pump but manufacturers don't support it. Some gas stations sell b20. If you're talking straight veg you need a certain type of injection system for reliability, and even there you're decreasing the life of the pump. Old mechanical pumps work great, first gen cummins, vw 1.6, mercedes om617 machines can run on straight heated veg for a long time with no issues. Electronically controlled mechanical systems like the vw 1.9 tdi can run on it too but might be a bit more finicky about what you're injecting.

Assuming you want to make your own bio you'd have to set up a transesterification process where you convert the trans fats out of the oil, that process uses lye so it needs a decent container and is best automated. If you're trying to recover the solvent, which is probably methanol, you'd need a still as well, and decent ventilation. Fully automated with raspi or arduino components is a couple grand or more, prefab units run something like 10k.

If rather than bio you're talking straight grease, it is cheaper to clean but more expensive to set up the car. You'd need a second fuel tank, preferably heated depending on climate, some solenoid valves, and a heated fuel filter. And a pile of hoses and wires to connect it all. Maybe a grand or so to set it up depending on driving conditions, kits run 1-2, some are better designed than others.

Either way you'd also want some big drums for holding tanks at home where you can let the fluid layers separate and a pump to move them around. Most car washes give away polyethylene 50gal barrels.

Most expensive thing in my opinion, is your time and the cost of the oil. You can get something like 5-50gal per week per restaurant, tho most overuse the oil. Best places don't cook meats in there at all. Chain and large restaurants want a schedule. Cost of the oil varies, used to be paid to take it, somewhere around 2010 that inverted and now you pay for the oil.