I completely understand not wanting to dress-up on a vacation--to the beach, no less! Especially if money is tight, less baggage is a great way to save money.
On the other hand, it seems to me that Disney is trying to strike a balance between its parks on one end and a fancy old-fashioned cruise line on the other. Case in point, the ships are decorated from stem to stern in a unified Art Deco/Nouveau theme reminiscent of a Cunard ship. Cunard=super fancy.
So what's the compromise? The MDRs are fancy, like a traditional ship, and Cabanas/Topsiders is casual, like a park. We wear our shorts and flip flops to dinner, then jump into the pool--it's vacation! Seems pretty straight forward to me.
I can also see arguing that the MDRs are a major part of the cruise experience. However, and how can I say this tactfully and without sounding elitist--trust me, we are no Rockefellers!???, if you literally can't afford to follow the cruise line's guidelines, maybe it's not the best match for you? I don't travel on Regent or Crystal because a) can't afford it the cruise fare (seriously!), but also b) can't afford the dress code requirements! I'd have to buy a new one-time-use wardrobe. To me, it's like buying a house without thinking about the other details, like maintenance. Sure, I can afford the mortgage...but I can't afford lawn care, power, electricity.
This will probably be an unpopular opinion, I know. But I DO want to have a vacation that's both family-friendly and somewhat "classy." Whatever that means. Although, I do know it doesn't mean workout clothes at dinner! Ugh!