I think Onkyo has some receivers certified for 4 ohm speakers in that price range.
Many receivers probably handle 4 ohm speakers regardless of what the manual says. But I would always question long term reliability to name one factor (some people think there's no issue at all with 4 ohm speakers.)
Note that 4 ohms is not a problem at all volume levels. As you increase volume, you increase current and you increase heat.
The output transistors, to name one factor are rated for so many cycles, which changes depending on output level. (The current passing through them will slowly cause damage over time.) The more you push close to their limit, the shorter they will last. Limiter circuits and heatsinking are there to help, but you have to ask yourself - if a receiver was not really designed for operation into 4 ohm speakers, over the long term, might lifespan be reduced?
I also have to ask, what about the extra heat which could result from operation into 4 ohm loads? Will this create issues with other components? I used to experience temporary HDMI failures on my Yamaha RX-V2700 when it got too hot. Surely a flaw of some sort, but makes me think...
On the other hand, people with reasonable listening needs can probably run 4 ohm speakers all day long with no issues. After all, average power levels needed while watching a movie can be really low.
Too bad there does not seem to be any definitive answer on this.
Audioholic's have an article addressing this. Seems like a bit of an oversimplification, but perhaps that's all we can expect with this potentially non trivial question -
http://www.audioholics.com/education...r-or-amplifier