The price point you're looking for is hard to combine with quiet places - prices are generally pretty high downtown, and any place that is quiet is likely to be pricey (i.e. a steakhouse or higher end destination place like Les Nomades or Spiagia). You might want to consider cabbing it to the West Loop or other areas for more options.
These places are on the edge of the budget you discussed, and aren't super quiet, but they're generally mid-range prices for downtown places:
Eataly isn't necessarily a Chicago place, but there aren't many around, and it certainly is an experience with loads of options. Go midweek if you can. You can get food at a wide range of prices.
Weber Grill is pretty straightforward, and they do a decent job with everything they make.
Slurping Turtle could work, unless that's too wild of a menu for what you're looking for.
Bar Toma is also worth looking at, it's become a go to place for me when meeting older relatives who are staying downtown. Solid options that aren't too wild, and reasonably priced.
Purple Pig and The Gage are both good options that are just a bit above the price range you mentioned. I wouldn't describe them as quiet (especially Purple Pig), although the Gage has seating in the back that is somewhat quiet.
Hopefully that's helpful, but unfortunately I think you may need to have a bit of give on some of your requirements, or expand the areas you're looking at to find better options.