I think new tires + alignment for under $400 will be tough. Most decent places want around $75-100 for an alignment. That means you'll have to find tires in the $50-60 range to stay within your budget. Don't forget, they'll charge you sales tax, maybe a tire disposal fee, cost for mounting, balancing, wheel weights, new valves and stems, etc.
In LA there are like 5,000,000 wheel and tire joints that can hook you up. Maybe 6,000,000. I moved away some years ago so I don't know the current number. But there are A LOT of tire places. I don't think mail ordering tires will save you much money.
My advice is to shop your local tire joints and see what they can do for you. Tell them your budget and what you want. They might have a deal with their tire supplier or can offer a nice discount on alignment. Chances are you're not going to get Michelins or other top brand but who knows? Shop at least 5 or 6 local stores and tell them you're ready to buy but need a smokin deal. I think you'll find one or two stores that will work with you.
