I hope your quotes include replacing the indoor coil or air handler, because you CANNOT install a 13 seer heat pump with an older coil.
The distrubutor cost of a 2.5 ton trane 13 seer is probably $1000 to 1200. The retail cost to you is considerably higher. The labor to install these will be significant. Don't know what rates run in your area, but this job could run anywhere from $4500 to $10000. If your numbers include the coil and the labor, I would say you are getting a good deal .