10 points = 1 increase in octane number.
If you mixed 1 gallon of 110 octane fuel to 4 gallons of 91 octane you would have 94.8 octane fuel
If you mixed 2 gallon of 110 to 3 gallons of 91 you would be at 98.6 octane.
1 gallon of race fuel is 5-6 bucks if you get it from a place that sells it for an honest price. How much is a bottle of desent octane booster? Like 104+ octane booster 6-10 bucks. If you mix that 1 bottle of booster in 5 gallons of gas (wich would be 4x stronger than what the lable says. Most bottles treat 20 gallons of fuel). So that 1 bottle might up you 1 octane number (10 points).
So 2 gallons of race fuel is a little more expensive than 1 bottle of octane booster, but the race fuel boost octane by 8 full numbers compaired to the 1 number that the booster does. Plus your burning a fuel instead of an aditive.