Similar to Bardo, I have had this discussion relating to my reptle-keeping hobby... But that aside, I'm coming to this discussion as a wife that had to buy her (then boyfriend) his first coffee pot... I feel your pain. When I first went out with my (now) husband, he drank office swill happily.. Until he had my coffee, then he started to be a believer. Now we make french press at home (when we have time) and use a drip machine when we're in a rush, but he has developed an appreciation for the "good stuff" and can't drink swill any longer.
All this said, I'd go all in and make your wife the good coffee.. Take the time to explain to her that you appreciate the good stuff, why it tastes better, and try to get her to try it with just half and half / sugar instead of the sweetened creamer she is using now. She may eventually make the move to good stuff w/o the creamer she uses now, but if not, you're still only buying / using the good stuff and if she truely only drinks a few times a week, she's not using up that much more of your good coffee.
I think, perhaps, from her point of view, she may be wondering why she can't have the "good" coffee you like and /or might not understand why you dislike her stuff. If you tell her that you want to buy the coffee and that you can both use the same kind, it might simplify matters... She may think she's doing the "right thing" by finding cheaper coffee and doesn't understand why it won't taste as good. Obviously, you want to say this in a gentle way (not make her feel lesser just because she doesn't like the good stuff now or doesn't understand the difference between good and bad coffee, etc.). When I started seeing my husband (the then swill-drinker), I let him have what I was brewing, even if he didn't appreciate it then, he developed a taste for it over time.
If her concern is the price of the good coffee vs. the cheap stuff, try going a middle ground... buy something like world market (I actually use their mocha java, Sumatra, and island blend as my normal daily coffee).. This stuff is better than, say, starbucks (and is actually cheaper by the lb.), but tastes better. Then you can get the really good stuff occasionally and get her try try the "special" coffee with you. If it is super important to you to use the best quality beans that are more expensive, then just explain how important it is to you and she should be OK with it, just make sure you leave room in your budget for a "coffee fund".
Good luck!