Jennifer,as for the wood paneling, I do not know for sure. My hubby has done cabinetry and fine wood work from real wood and personally I would fear real wood or wood paneling would warp in time. I also have read about this possibility. I will not use it but I know they did many years ago. A Masonite hardboard panel is primarily processed wood fiber. I have a printout from someone who wrote, "Tempered Masonite is much stronger and, once it is carefully sanded will provide a strong mechanical bond with the paint." And added, "I have panels that are over 30 years old which have gesso, egg tempera and embellished gold leaf." There is no sign of cracking or damage.
Price? I buy locally but Lowes has it too and I pay between $8 and $11 for a sheet, 4x8' sheet. I have a friend who uses it all the time and has for many years and her portraits, florals etc bring in excess of 4-6 thousand dollars.
One real good reason that I love it too is that it is so simple to frame. No worry about the depth of the rabbet. The Masonite is 1/8 in. or 1/4" thick and will fit into any rabbet depth very securely with offset clips.
Good Luck,
Patt