HDMI converters can be obtained for network cabling and for composite video-audio but not a 2 conductor rg cable that I've ever seen. There are slitters for HDMI but any way you slice it both tvs would would have the same signal at the same time, i.e. no independent control.
ROKU units are often very reasonably priced and easily obtained. WalMart, Home Depot, most big box stores and many smaller stores sell them. Of course they are available on the web and typically on sale. Now days you could likely pick on up for less than the cost of 2 doz eggs.