White Robes

At my school, boys wear navy and girls wear white robes for graduation.
Since the robes are white, girls have to wear a light colored dress (preferrably white).
The darn people who chose white robes didn't know how hard it is to find a good white dress!
Sure I've found a nice off-whitish colored dress, but it's pretty see-through, which is not what I'm going for.
Oh, and there's another problem: Shoes!
Since we walk on the football field, they want us to not wear spiked heels, but flat shoes that are not flip-flops.
Where am I going to find affordable, flat white sandals?
Everywhere I go, i find affordable white sandals with spiked heels and expensive flat white sandals.
Is anyone encountering the same problem?