Is there a notice board there that you could put a notice on??

You may find a mum / dad with a girl a couple of years older than yours that would happily pass them on at a small cost as their child grows out of them.  Certainly can't hurt to ask.. 

can you sew???

bike shorts are easy to make. a normal singlet top will do.

Maybe try rebel sport or another sports store, but I know kinda pricey.  You could also have a look at a Salvo's or St Vinnies store.  You might be able to pick up something cheap there...