HDMI to cat-5 converters are not inexpensive.
If you can live with 1080i video, I have used first hand the Monoprice version...
http://www.monoprice.com/products/product.asp?c_id=101&cp_id=10105&cs_id=1010504&p_id=4065&seq=1&format=2
Though currently on back order, your price is almost a wash compared to buying a HDMI cable that long. Likewise, you are likely to get more consistent and reliable results with the HDMI->CAT-5 extender than you are with any standard HDMI cable.
Does it work well?
That's a tricky question because, at the end of the day, HDMI sucks.
I mean, it's great...
But it sucks.
HDMI has all sorts of tricky little crud built into it to disallow multiple connections, multiple hops between locations, multiple repeaters, multiple splits, etc.
As a real bonus, you have absolute NO clue what it actually DOES allow because every single device you own which uses HDMI can respond differently.
Actually, being more specific, HDMI could be great, but the HDCP on the HDMI screws everything up.
A few companies out there have the ability to maintain true 100% sync with HDMI devices while running them through a HDMI matrix switcher, but the price on those products is insane.
At the end of the day, right now... I use a component matrix switcher to allow my 5 HD destinations to access eight (or so) component video devices in my home and it works flawlessly... except for the darn scan lines I get. If I was really smart, I would convert every component source to HDMI using a scaler then send it over cat-5 to each TV.
That wouldn't be cheap.
I've got no guarantees when I can't design the product myself. Sorry.