2.5-10 power optics are somewhat popular but everything varies based one what participants can find/afford/likes. I don't know of any in your price range though. I run a fixed 3x and it works well for me for SR.
In your price range I think you should look at consider Bushnell, Nikon, Vortex and possibly Leupold. I think the first two have AR type scopes in your price range, the others for just a bit more. I don't keep really up to date on optics prices because I am not in the market. Keep an eye on the EE for used options as well. For most scopes, you will probably want some type of cantilever mount to shift the scope forward for eye relief.
I agree that target turrets are your best bet but if can't find something you can afford right now, you can work with a BDC reticule. Regardless, plan on recording your zeros / hold overs for various distances we shoot at. You can then refer to these at subsequent events.
IMO - its better to get a less than optimal optic that you can afford and get into the sport sooner, rather than waiting for better/optimal equipment. You can always sell a scope if you decide you want something better later to help pay for your next purchase. During the season you can talk to other participants and check out what they are using. Most folks are very accommodating in helping each other out with stuff like that.
If you can, get an optic and get to the ORA SR clinic in Borden in April. It will give you a leg up on starting in SR regardless of the CofF used at an event. Not required but a benefit. I know it's a drive and all but I'm traveling from Barrie to Connaught 4-5 times this year for matches so it's totally doable.
Clinic or not, come on out and shoot the ORA matches at Connaught. Don't worry, nobody has gotten lost with the CofF yet.