If you want a cheap flight from Doncaster to Chicago, you've got zero airlines to choose from.
Chicago Midway Airport is just one of the airports in Chicago. If you're not set on a specific airport, try changing your search from Chicago Midway Airport to Chicago to see a broader range of flights – they might be cheaper.
You can expect accommodation prices to be higher at this time of year too. Last-minute deals do crop up, but it's best to book everything in advance to avoid disappointment.