I don't think you'll be making the most out of OsakaNoHonma's fantastic resource if you plan on Udon for lunch.

Udon, generally, will cost the same in the evening as at lunchtimes. Noodles, okonomiyaki, department store bentos are all good bets for evening dining.

The magic of the blog is that it will help you find places to eat where the food will cost between 1,000 & 2,000yen in the afternoon yet a similar menu will set you back around 10,000yen and upwards at night.
Lunchtime specials can be an amazing bargain allowing you to eat some of the best food in the city for a pittance.
I'd suggest: http://blog.livedoor.jp/osakanohonnm.../50954776.html
labelled 5* 月波 lunch 1,000 on the map
or
http://blog.livedoor.jp/osakanohonnm.../50423464.html
labelled 5* 日本料理 遠藤 lunch from 1,000

or here:
http://blog.livedoor.jp/osakanohonnm.../51262072.html
the keiseki style menu where the portions are brought out one by one was 3,300yen (not a bad deal at all!) or you could go for the kaisendon (menu on a tray if you scroll down) for 900yen
labelled 5* 秋やま 3,500/900

All are labelled with the green icon on the map.

If you're dedicated, you could eat pretty well for about 3,000yen a day. Go somewhere high end at lunchtime and try the more moderately priced options in the evenings. Department stores will often discount food just before they close up, a bento could be a good evening meal or just look for cut-price pastries for breakfast (pop into a paper bag and blast with a hairdryer to freshen up). But don't miss out on the glorious patisserie even though it is full price, you'll find some of the world's best desserts are very affordable.

I'd suggest 5,000yen if you really want to make the most of Osaka.

Have fun, and please do report back!

Well let's see....

Coffee: Anywhere from 100-500 Yen average. Fivebucks is everywhere, as are doughnut places, and trad Japanese Kisaten.

Breakfast:If you don't like what is on offer at the Swissotel then take a wander to a conbini(7/11) for a onigiri (rice ball) and a canned/bottled tea or coffee. Shouldn't be more than 300 Yen for that. If you are game ask the concierge to find you a restaurant that still does "morning service" where you get a modified American breakfast for about 5-700 Yen.

Lunch: Bento (boxed lunch), a multitude of choices and prices to fit most budgets. Expect to pay from 3-700 Yen. Noodle shops are a good value for lunch as are most restaurants. Noodles from 250-1000 Yen a bowl(depends on place and what you order), you can ask for more noodles if you have soup remaining "free". Swank restaurants often have discount menus for lunch that are extremely good value. Sushi, can be had for about 150 Yen for normal stuff, price goes up according to fish quality.Cheapest would be at sushi conveyor place. Or failing that try and get to a fish market early in the AM to try !

Dinner is Yakitori, kushi-katsu, negi-yaki (savory pancake), Yaki-Niku. About 3000 Yen to eat your fill including a mug of draft beer or a glass of Japanese sake /shochu. Usually pricier if you want Japanese marbled beef at a steak teppan place.

Alternatively...

You could shell out 17,000yen and get this: http://blog.livedoor.jp/osakanohonnm.../51521712.html
you even get fugu in the deal

I'd probably stretch my lunch budget here: http://blog.livedoor.jp/osakanohonnm.../51519249.html (3,675yen for this menu)

And don't forget that ordering beer, wine, sake or soft drinks can double the price of a lunch menu. Remember that some sort of drink (tea or water) will always be included.

You can get dinner for Y1000 if you want. Whatever your budget is, there will be someone who will serve something. We have a place across from the hotel that fills you right up for Y880 and the hotel can set you back Y20000 if you want.

Shakey's pizza for Y900 all you can eat plus the coldest beer around for Y250.

And how could I forget...there's a Brazilian all you can eat steak, prime rib, chicken, pork, sausage, lizard, dinosaur, etc that we are ALWAYS willing to go to. Y2415 until you're stuffed. It also has a great view of the harbor just a short train ride away in Kobe.