I got married 4 years ago and I love wedding talk! Expect this to be long!
When I got married, I wanted something 'different,' something other than a banquet hall. I was looking at restaurants, gardens, mansions, everything - downtown and suburbs. Asking about a person or dollar limit is key. Finding out gratuity and tax is also key to the budget.
Honestly, one of the best deals for small parties that I found was the Sears Tower. I got married 4 years ago, so maybe things have changed drastically, but at that time, it was a Levy run place (I didn't see it on their site tonight, however). The room was the entire 99th floor, room rental was $1500-2000 or so, and the entrees ran from $75 for vegetarian -150 for filet with a $5K min. That included tax & tip - making it very much in the financial realm of possibility for most people, and very attractive to smaller parties with the low minimum compared to other places*. I was shocked at their prices, to be honest. The only issue would be a cloudy day, although they assured me (true or not) that they never had an entire event that was 100% cloudy - that it usually was earlier or later in the event and at some point, the view was exposed. I do remember their kids' menu to be terribly expensive - something like $56 per child for drink, food and dessert. That is what ruled it out for us, we really wanted kids to attend, 25 of them vs 100 adults (when other places charged $6 a kid) and it was just cost prohibitive at that point to invite them, so we chose elsewhere, in the suburbs, close to home. I paid $85 pp with tax and tip at Prairie Rock in Elgin - and it was a cool place, with good food (great apps, salad, filet, potato, veggies, cake and ice cream) , and unique. We even did brewery tours during the cocktail hour, which was cool. They only do about 10 weddings a year, so their service kind of stunk (they served our cake top! Among other things...), so you may want to ask how many weddings they do a year to get a gauge of how much wedding experience they have. (not every place includes the wedding cake. Be sure to ask, and even ask about cake cutting fees. Yes they exist!)
I would also highly recommend picking up a Chicago Bride magazine. In the middle there is a section that lists good places for b-parties, rehearsal dinners, and weddings. It lists the place, room sizes available, minimums, entree prices, etc... for places in the city and suburbs. I would even consider looking at the rehearsal dinner places as those tend to be smaller parties, so that may be more appropriate for a smaller wedding dinner.
Last but not least, I would recommend just calling the places of interest and asking them if they have hosted parties of this size and what they can offer in terms of cost/menu/room selection. I did a lot of that. I almost had mine at a tapas place (I considered two). One I ruled out due to the room being small and tiered, which was just too complex (then they closed - dodged a bullet there!). The other was a many-room set up, dancing here, dinner here, smoking here. I ruled that out due to wanting to be able to look across the room and see my groom, or dad or grandma and make sure they were having a good time. You can't do that if people are navigating many smaller rooms. But in some cases, it works and the bride is ok with it.
I am sure I have given TMI here, but I loved planning my wedding (yet I was not a bridezella!), and I really like helping other people see all the options available to them so they can have the wedding they want.
Oh, one last thing! Check out the Chicago Park District. They have many gorgeous sites available. You have to ask if they have preferred vendors, or if you can choose your own.
Good luck, and keep us updated!
* For instance, 4 years ago, the food & drink minimum at the Crystal Gardens at Navy Pier was $28K. The Saturday rental rate at the Chicago Bortanical Gardens was $11K. That didn't include one drink, one appetizer, one chair. It was just to reserve the space! The rest still had to be paid for!