Actually, there is a cheap way...
It's a little known fact that most of the autodimming rearview mirrors with homelink built-in are made by one company -Gentex.
To make things interesting, they really only have two models - an older one which have painted buttons and a newer one with injection moulded buttons (and slightly better autodimming). There will be a bit of variation between the mounts but most japanese cars and some North American use the same mount that Subaru has and the wired harness to connect the mirror to the car.
Knowing the above, you can buy an used mirror from e-Bay/autowreckers for under $100 (many times for under $50), buy the wiring harness as well as the windshield mount adapter (if the autowrecker didn't have it with the mirror) from an online parts place and do the install yourself!
Here's a website that spells out the mirror models -
Welcome to WembleySells.Com - Gentex AutoDimming Mirrors - Gentex HomeLink Mirrors - Gentex Mirror Customizations - Valentine One Radar Dector Mirror - Gentex Mirror Installation Instructions
Here's the Subaru model number for the harness - H501SSG010.
Here's the Subaru model number for the windshield adapter - H501SSA040.