I'm not doing the race but did the Delmo AC OLY event a couple weeks ago. I'm not aware of anything available except the casino hotels which will cost you at least $250/night. And then I would feel safer taking a cab/uber rather than walk the streets of AC in the dark. There are many decent motels on Rt 30 for about $50-60/night and about a 15-20 minute car ride in the morning to parking at Bader field.

I've done many DelMo events. I almost always stay on the boardwalk, usually the Tropicana, and I walk in the mornings. I've never had an issue. I usually walk down the boardwalk to Albany Avenue and then follow it to Bader Field.

I just booked the Quality Inn Flamingo. Looks to be one block off the boardwalk and next door to the Tropicana...but just $180/nt.