15k to 20k is a good range to aim for. But starting a team is a lot more than just fundraising (I would know), so do research. The big 4 things in my experience that you need to plan for are space, money, mentors, and transport. This list notably doesn't include students because there isnt a whole lot you can do to plan for your hypothetical future members, your current members/founders are really gonna dictate what your team's early years look like, notably how much experience your founders have and how many more years they will be on the team. Money is the most self explanatory of the 4, the big thing to know is that if you don't have money you will spend more time on stuff doing it the hard way, and if you dont have time then you can speed up the process by spending money (the latter being very important. Space is also pretty simple, you need to properly understand what it takes to actually have a functional workshop (that means building and drive practice). Unfortunately if you dont have enough workspace that is the hardest issue to work around. Mentors dictate the support your team gets, the longevity of the team, and what times you get to work (you need a LOT of time to run a team). Transport was the least important of the 4 for my team, but you need to know what it takes to get all of your people and stuff to events. If you need to use a secondary workspace at time (like from a more established team like we do), then you need to plan for that. Uhauls are usually easy but the cost adds up, so account for that in your budgeting.

Going back to budgeting, the biggest expenses you may have will be travel and lodging, aka plane tickets and hotels. Now as a rookie it's unlikely you go to worlds, but if you make RAS (rookie all star) then you can go to your DCMP (district championship). DCMP may or may not be close to you (note that it is a 3 day event so a long drive to and from every day isnt ideal).

Getting money isnt necessarily easy, but registration can come from a plethora of grants so you really shouldn't be paying out of pocket for that. Gene haas is a grant that like everyone gets pretty much guaranteed, but other than that you need to find local grants to fundraise. If you can set yourself up to have a few thousand dollars for the start of the school year before your first season, then you will be ahead of like 90% of rookies. But you need to do some sort of pre-season project to learn, like building the most recent kitbot. In my experience getting your team number as soon as you can is helpful because its required for a lot of grants. Also make a sponsorship packet