Gas or electric?

I have a raised ranch with the living room on the second floor. We have a prefab fireplace in the living room,
We have a pellet stove on the lower level and we have forced hot air. Oil is out of sight. Electric cost about 16 cents a kwh. Pellets are the most reasonable. This winter, my wife is complaining about being cool. When the outside temps go into the teens, we need to assist the pellet stove.
We have been discussing putting a propane gas unit in or in front of the fireplace. My question. Are there advantages to the insert or the freestanding unit? Or will the cost for an electric space heater be about the same? Open area about 28 x 20. Well insulated.
Thanks

If pellets are a more reasonable way to heat in your area, you could install a pellet insert into your wood burning fireplace. As with a gas insert, it will be necessary to install a liner kit from the stove through the chimney. Measure the maximum opening of the fireplace (doors and trim removed) front and rear side to side, height and depth and take them to a local dealer who sells pellet stoves. I think it would be better to use the fireplace rather than install another unit in front of the opening. Another option would be to go with a propane insert, you will need to take the same set of measurements as the doors and trim will be removed. We offer a nice selection of vented gas inserts on our website gas-fireplace.com. I would be hesitant to recommend electric heaters or fireplaces as they operate at 4600 BTU's and just don't offer enough heat for most applications. The BTU level realistically will heat about 200 sq. ft., enough to add heat to a room with an existing heat source.

Since it is only your wife feeling cool and (not you) an option is to simply get one or more small electric space heaters and simply locate them next to her where she spends a lot of time (by a living room chair where she relaxes/watches TV, by a computer desk when she is on the internet...)

and that is what I have been doing. Looking at all my options. Thinking I really would like to see some heat in that fireplace, but need to be able to afford it.

16 cent/kWh elec is the same cost/BTU as $3.25/gallon propane at 78% eff. What does propane cost in your area??

as noted earlier, propane cost is all over the place. Low end users pay nearly twice what high end users do. I think the cheapest I have been told is a bit over $3 and nearly $5 for the occasional user.
If I were to do it, I might opt for two 20 or 30 pound takes used together like is done is travel trailers and fill tranport them to be filled myself. I hate being tied to any contract.

Stay with electric. It is currently your cheapest option.