The choice between MRAD and MOA has been debated for a while here. One really isn’t better than the other; it just comes down to personal preference. The most important thing is to pick a scope with turrets and a reticle which match. This isn’t as big of a deal now as it was a little while ago as most scopes manufactures make sure to match the two, but there are still some scopes floating around with MOA turrets and a MRAD reticle so avoid those. With that being said it does seem that at least for tactical scopes, MRAD is more popular than MOA. My opinion is if you have to learn, you might as well start off learning on a MRAD scope. I would also highly recommend getting a scope with first focal plane (FFP) reticle so that the reticle subtensions cover the same distance at a given range regardless of what magnification the scope is on. These cost more, but are well worth it.
Some potential scopes in your price range would be the SWFA SS in 3-9 or 3-15. Both are under your price limit have a reputation for being reliable and repeatable scopes with decent glass. The 3-9 is about $100 less than the 3-15 but if it were me I would go with the 3-15 for the extra magnification range. Both of these are also only available in MRAD. A scope from the Vortext PST line would also likely work for you. They are offered in both MOA/MOA and MIL/MIL, with an illuminated reticle as well as FFP and SFP. Going with a SFP will save you a couple hundred bucks but I would highly recommend paying more for a FFP version. The price will vary based on what magnification range you choose but any version that has a top power between 10x and 24x should suit your purposes just fine. You can also look at some of the lower end offerings from the Bushnell Elite Tactical line or something from the Weaver Tactical line. There are a lot of very good scopes out there. These are just some suggestions that fall around your price range from reputable companies with good warranties and should get you off to a good start. Searching this site for the scopes I mentioned should bring up tons of reviews and comments to help you learn more about each one.
When it comes to finally purchasing, some of the sponsors of this site will sometimes offer you a better price if you call and say you are a member here, so look and call around and you may be able to save a few bucks. One last option would be to go to the optics for sale section here and search. Often guys are selling very good lightly used scopes at a hefty discount to new. It is worth a look as you can get some good deals.