I would stay away from the gunshows. They are fun to go to, but the prices people put on their wares, you'd think that they are made of gold.

Cheapest way to get an AR:

Order a stripped lower receiver from an online source and have it sent to a FFL holder for the paperwork- find a FFL holder who won't charge you an arm and a leg for the transaction, from my asking around, prices for this service range from $15 to $100. Anything over $30 is pretty much a ripoff. The lower receiver will cost you about $100. this site has one for pretty cheap: aimsurplus.com

Order a parts kit for your lower receiver- this can be shipped to your house.

Order a complete assembled upper to your home.

Put the thing together. It takes a bit of time and effort, but it doesn't take a huge amount of skill. If you do a search, you can find videos and books that will show you how to do it.

If you go this route, you will save at least $150-200 over buying an assembled rifle.