Just for a reference, a neighbor just added a baggage door to an early Cessna 175 that did not have it. A company had produced an STC kit using all used Cessna parts from later models. No one has done the same for the early Travelers, so it would be expensive to get a DER to build a packet to get the approvals for the mod. My neighbor probably had 15+ hours in the installation on the Cessna. I would expect it would be the same for labor on the AA-5.