I was thinking of doing something, but wasnt sure if anyone made what I need. I am interested in having my cable box set on a channel.. then have a wireless signal sent out to my upstairs tv. To avoid having to own 2 boxes.
Can it be done?

There are many availble, but here is one.

http://www.smarthome.com/76540.html?src=WG1002552

... or for ~$5 a month, rent a cable box. After 3 years, you break even on the price (+shipping) of an extender. :)

Its $8 and change here a month for an extra box.

Is there any way of doing it with a wireless router!?

I was thinking of doing something, but wasnt sure if anyone made what I need. I am interested in having my cable box set on a channel.. then have a wireless signal sent out to my upstairs tv. To avoid having to own 2 boxes.
Can it be done?
You can get 2.4GHz transmitters for much less than this 5.8GHz model (http://www.bhphotovideo.com/c/product/330515-REG/RF_Link_AVS5811_AVS_5811_5_8_GHz_Wireless.html) but most people find the amount of interference with them to be unacceptable.

I just ran an extra coax cable from the HD DVR channel 3 RF output to an analog TV in another room. Output works simultaneously with the HD output from the box to the main HDTV.

If you can run a coax from the box to the other room you can control it with "pyramids", see X-10.

Is there ANY way to backfeed a signal through the same line coming in?

No.

I cant see why not. There is a signal going in both direction anyway. Please explain your NO response

You're right. The line feeding the cable box has a bi-directional signal, but the "other direction" (the return path) transmits directly back to the office (headend). This return path can not be used by the user in any way.

- Cable Tech

I cant see why not. There is a signal going in both direction anyway. Please explain your NO response

Any channel you are likely to be able to back feed on - is likely already in use by the cable company.