Need help about school project

Me and my friend are trying to make an autonomous drone without GPS that can go inside the school, but we are not sure which flight controller or which software we should use. Among our preferences is to use a raspberry pi with a pixhawk, but I saw a radiolink mini pixhawk on the internet for half the price of a fake pixhawk, what should I do? (maximum budget is $200) or is there an easier and cheaper system than this one? If so, what are they?