Overbid to an extent, with good justification, because you may not get all you want.
Make a list yourself with fields 'urgent' 'important' 'cost'. Not everything important will be high cost, and not everything high cost will be important. Stay credible, but overbid a little. Really break things down in your Work Breakdown Schedule so everything's within +/- 5% in estimated cost, so you informally have a good idea of your budget provided, and you overbid by about 10% or more depending on your experience on how bidding works in your school.
I totally agree with the above suggestions on creating an environment. Make a vibe, a buzz. Have small low cost events too. A secret santa programming contest making a Christmas or Easter website. A legacy PC with Lynx. Whatever.
And make sure everything of value locked down if you think that's a risk. Not imposingly, but I remember in the 90s my class would strip down a PC when the teacher's not looking, from taking a strip of RAM to switching a DX100 for a DX33 [or something like that, it's a while back].