As bakes65 pointed out. Your initial kit cost will be less than the other stuff you have to buy for it.
Read what comes with the kit before ya buy.
Does it come with wheels? (if it does and they are little guys like 1 1/2" you'll want to replace with bigger if you fly off grass)
Fuel tank?
Silicone tubing?
Motor mount?
And by the time ya buy CA/ epoxy/ Couple rolls of covering etc a kit can double in price real fast. BUT!!!!
Even though you might think I'm discouraging you I'm not. Building is a blast, it's rewarding, it's a learning experience, It's addicting, It's an outlet for imagination.
BUILD ON GUYS!!!