Aircraft Spruce usually seems reasonable to me. I haven't bought any bolts, but I just received an order for mil spec screws, coax connect connectors, etc., and it all seemed very reasonable. 100 count bag of short MS35206 screws for $6. That is about the same as what I pay for cheap hardware at the big box stores.
One thing to be aware of with Spruce is that if you have parts coming from two locations, you'll pay shipping from both. I missed that, and paid $8 to ship that $6 bag of screws from TX. The other $80 worth of stuff came from AZ and shipping that was also $8.
Still, $8 S&H is a bargain these days.