When you purchase an old unit, you are not entitled to any updates for free.
Assuming that the unit does what you want it to, then you either update the map one time for $40 (per your post) or you get a lifetime update (lifetime of that unit).
Except for new nuvis that may be entitled to one free map update, Garmin requires either a numaps One Time map update (probably not worth the expense) or a numaps Lifetime purchase (about $60 or so which will entitle you to up to four map updates per year for the life of the unit--you will need to decide if this is worth it. Due to a good combination of features, these units are better than most later nuvis, especially the inexpensive ones. Also, 5.30 was released a very long time after the model was discontinued.
Keep in mind that with a bit of patience, you could find and buy a new nuvi with Lifetime maps for under $100.) Should you decide to update the map, please let us know before you start because there are things you should do before trying the map update. It may be worth the sixty-odd dollars for a Lifetime update. Garmin does release firmware updates for discontinued GPS models.
Remember that the lithium-ion battery in this unit probably will need replacement in the future. I have had so many problems trying any new firmware from Garmin for the discontinued 750 that I concluded that Garmin's software group does not own any 750 units anymore.