I wouldn't drop the gender designation. Age group awards are a tough call because a lot of people will be disappointed if you don't "spread the wealth". I like Andrew's idea but I'm not sure how popular it would be overall.
One thing to think about, you can get some nice paper and there are incredible things you can do with a good computer program and printer. I have a couple of certificates from races that did those in place of trophies, medals, or ribbons. If you had access to a laptop and a reasonably small printer and you had a power supply at your disposal, you could even come up with a template that would allow you to print names and maybe even times on the certificates before the awards ceremony. I'd want to take a few dry runs with cheap paper/ink to ensure you have it down and can do it quickly but that might be a way to cut costs and hand out something that would be pretty unique. I'm not sure what the cost would be but I'd guess less than trophies and medals, maybe even less than ribbons.