How upgradeable do you want it?
For someone who just wants a decent home theater on a budget and isn't looking to really get into serious home theater in the future. Go over to amazon and pickup the HTS3400 maybe. It's only $250.00. The sub is passive(powered by the receiver), the receiver doesn't upconvert non hdmi signals and it's not very upgradeable IMO because of that. But I think it's a great system for people starting, people who aren't going to be upgrading, or people just on a severe budget for right now.
Another Onkyo option under $400 is one of the refurbished systems at club onkyo. Think they have the 5400, 6300, 7200 all for under $400 when you sign up for club onkyo which is free. The plus with any of the more expensive Onkyo setups is you're getting a receiver that is going to be a great foundation for future upgrades if you're pondering that and usually loaded with options. Heck even the 3400 I spoke of above has some great options on the receiver.
Monoprice has a cheap 5.1 speaker setup for $85.00? I think. You could pair that with a receiver. However that speaker setup is on backorder currently. But gets a great reviews.
Similar Parts express has a 5.1 speaker setup for $169-$199 depending which size sub you pick(8"/10"/12") and you could pair that with a receiver for $400ish.
Amazon has the boston acoustics classic 5.1 system in black for $199.99 you could pair with a receiver.
IMHO if you're spending $500 or more you can get better quality speakers than HTIB or satalites in general and a receiver almost for that. I personally wouldn't pay that much for a HTIB and rather instead start building a better quality home theater at that point..
None of the above have wireless rear surrounds. No decent quality htib I know of does. So you'd be on your own for that. But I believe rocketfish or someone makes wireless rf adapters.