Please do yourself a favor and don't consider buying anything that is not lace front and 100% human hair. If you are serious about passing, I promise you investing in a good wig is well worth the cost.
You can get a decent lace front human hair wig for about $150-$300. My advice for you is to go on YouTube and look up African-American hair gurus. They all specialize in showing viewers how to install, blend, and make the wig look as most natural as possible. The majority of black women you see in public are wearing a type of hair system or another, so they typically know more about wigs than anyone. No point in buying a wig if you don't know how to install it.
Some personal advice is to also get a wig that has a "silk top," meaning the wig actually emulates the color of your scalp to make it seem like it is growing out of your head. Silk top wigs typically run more expensive for the very reason that they look more natural.
Also, the most important thing women fail at in making their wigs look natural, and this is the case for many women I have seen here on Susans, is that their wig has NO visible parting that shows the scalp. Nothing screams more "wig!" than that. Basically you will want to get a pair of tweezers and literally tweeze out the hairs from the wig to create a visible parting. You want the top of your wig and parting to look like this:

Please also only buy 60-80% density wigs. 100%-120% density wigs are very full and look wiggish, even if they are human hair.
Last advice, bring your hair to a salon and have them fix it, put layers in it. DO NOT simply buy a wig online, install it, and think you're good to go.
Some good websites for wig shopping:
rpgshow.com,
bestlacewigs.com