Auctria is an affordable option, although not as intuitive and will take someone dedicated to making it respond the way you intend. It's not bad, just takes a bit of time to figure everything out on your own.
Bloomerang bought Qgiv a few years ago, and that is the next affordable option. It has more robust offerings and better support. Sometimes you can subscribe to the auction portion just for the few months before and after your event rather than the entire year, if you only have one event. This option has better support and a more polished experience for donors and volunteers, but it does push everyone to download an app for bidding at the event. I have found that it is the preferred platform for several organizations, so savy donors are more likely to already have it on their phone or have experience using it.