Travel
Hotel
Mission Inn Hotel & Spa
Hotel
Marriott Riverside at the Convention Center
Hotel
Hyatt Place Riverside/Downtown
Hotel
Hampton Inn Riverside Downtown
Flight
Ontario International Airport
Ontario Airport is the closest airport to Riverside and is around a 30 minute drive away. Because it's a smaller airport, the tickets are usually higher but it's worth taking a look. The airport is really small and extremely easy to get in and out of. This is your best option if you're looking for the easiest flight and are okay with spending more.
Flight
Los Angeles International Airport
LAX will probably have the cheapest flights but will be the farthest drive to Riverside and that's not even considering the traffic. LAX is anywhere from 1 hour to 1 hour 30 minutes from Riverside. LAX is a gargantuan airport and a pain to get around but if you're really looking to save money then fly out of here. Just remember, you're gonna pay in other ways.
Flight
John Wayne Airport-Orange County
Santa Ana might be the goldilocks airport for getting in and out of CA. The travel time is around 45 minutes to 1 hour 15 minutes to get to Riverside. It's comparable in size to Chicago's Midway Airport and is easy to navigate. The prices will be a little bit more then flights at LAX but cheaper then flying into Ontario.