Well after all the tests, trials and failures I had last year trying to shoot youth basketball I finally ended up with what I believe to be the best basketball lens for me. The Canon 24-70 f2.8L on my 40D crop body.
When the season started last year I had a canon 50mm f1.8 that I tried to use. I did end up with a couple keepers, but I knew that wasn't going to work fo me. Too slow to the focus.
Next I rented a Canon 50mm f1.4, also too slow to the focus and even though it has a USM focus motor (well not really, it's a Micro USM motor)it was a horrible Bball lens I thought. Maybe it was just a beat up rental lens, but I had more keepers with the f1.8 version sad to say. Then I tried adding light to the court. That helps more than anything I had done to that point. I also tried using my 70-200 f4L. I found it to be just a bit too tight on the 1.6 crop body.
So then the seach was on. I needed to find something that was fast (f2.8 or better), fast to the focus (it needs a USM or equivilent drive motor) and it had to be sort of wide as well. This left the Canon 24-70L or a Sigma 24-70 f2.8 HSM to consider.
I chose the Canon 24-70 f2.8L because it was a Canon lens and more than likely wouldn't need to go back to the factory to get ajusted before I could use it, even though it would be a new lens (a round $900 new). And I found a great deal on a Canon refurb lens through Calumet Photographic. I paid $1100 for my 24-70L and I haven't ever regreated it once!
I found the zoom in that range to be perfect for under the net/baseline work. I know it's not in your price range, but it is a wonderful lens for Bball. It tracks and focuses so fast and is so amazingly sharp. On your 7D it'll be really great!
Then this past spring I found a used 85mm f1.8 and I can't wait to try it out this winter. I think it'll be best used on a crop body from the corners. It'll be too tight for under the net action for use on the center and forwards, maybe gaurd shots from ther top of the key, but it'll be great from the corners. For the $400 or so that the 85mm f1.8 will cost you (I got mine for $340 used from www.KEH.com ) it will probably produce some excellent images for you if you can't spend for the 24-70L.
My other suggestion is to look into adding some strobes on wireless triggers to help with stopping the action and getting better images. Most gyms, even HS and College gyms are horrible for taking action shots. And if you're taking shots of youth players, don't let anyone tell you that you'll be fine because they are slower. OK, maybe a bit, but it's not like they're old folks in wheelchairs either. It's a fast game and when played right, it happens very quickly!
Canon 50mm f1.8
Canon 50mm f1.4
The reason I didn't like the 50mm f1.4, it totally back focused this shot.
With lights and a Canon 28mm f2.8
Canon 70-200mm f4L with lights (not enough)
Canon 24-70 f2.8L with lights (shot @ 43mm)
24-70L @ 32mm with lights (4 strobes in all)
24-70L @ 35mm with lights
I know these are a little too wide, or un cropped, but I never know what a parent will want, so I leave them a bit wider and can then work from there.
I'd say get the 85mm f1.8 and a couple of strobes with a cheap wireless system (I use the YN RF-602 and it works great!) and have a whole lot of fun this year!