The f/4 aperture will be insufficient. In your budget I'd recommend the EF 100mm f/2 USM. If you feel you absolutely need something a little longer, the EF 200mm f/2.8L II USM - but, even f/2.8 is sketchy in gymnasium lighting. The EF 135mm f/2L is the 'ideal' indoor sports lens, but a bit outside your stated budget.