You could try the Luthy Botanical Gardens near Glen Oak Park. I have no idea what it would cost but I hear it's a beautiful setting. Another suggestion, contact some photographers in Peoria as I'm sure they would know of all the places to get married outside as I'm sure between all of the photographers they've photographed weddings at all of them. Good luck!
the Scottish Rite Cathedral is pretty reasonable. It is an old building with a lot of the traits, both good and bad, that come with older structures. The windows are amazing in the sanctuary, and you could hold the entire event in the downstairs room if you wanted to.It's also very easy to get to and has ample parking. The Knights of Columbus hall on Radnor road is also a great space but not sure about price.