There pricing is a little confusing so I have sent an email to sales. Looks like it is going to be too expensive so another alternative I saw was to have Mac people run VMWare or Parallels.
Another option to FM Migrator is to export your access tables as excel files and then import them into a FileMaker file. This puts more work on you, as you'll have to create the necessary relationships yourself, but if the access system isn't too complex, this may be doable.
Haven't used Migrator either, but given the differences in how Access and FileMaker do things, I'd expect you'd need to do quite a bit of design work in the FileMaker file to replicate the function of the Access system even if you used it to migrate your data and tables.
On the flip side, once you had a FileMaker version working, you can run it on both Windows and Mac systems and can scale up to a server based system much more smoothly than you can with Access.