I would say, that if you already own a 70 gallon tank!! than you're in a decent position to get hooked onto one great hobby. But one post, or ten posts can't accurately determine if you and your wife are going to enjoy a marine aquarium. Or can afford it.
The big question is: Was this tank purchased new, or did you previously have tropical fish, and are now moving up? Although it is not required, many first start with tropical fish and switch to marine, after a period of experience.
Although many will suggest that the cost gap between tropical and marine aquariums has closed over the past two decades, to me, the cost difference is still real.
But you have found the premier source of friendly, experienced saltwater hobbiests here, at the message boards. And the online store is top notch, too. (From my experience.)
If you read the posts on this forum for a couple weeks, purchase some decent resource books, such as "The Conscientious Marine Aquarist" (You can get it through this site!), and exercise patience, you could easily manage a FO (fish only) tank for around $1000. This is just my opinion, and most would not quote a price. But I am thinking you already own the tank and light, and not the filtration, heater, salt, sand, fish, etc.
I have a 36 gallon FO. I've spent about $400 so far, and that included the tank and light. I would have spent more if it wasn't for this forum.
I hope this helps.