I'm an insurance agent, let me clarify a few things:
1. Most Homeowners (and renters) policies will have SOME coverage for guns, but it's very limited. $1000 is common... and as most of you know, that's not nearly enough.
2. Most Homeowners policies offer the option of adding an endorsement (rider) to the policy to cover items like jewelry, furs, and firearms up to a very high amount. The cost will be built into your homeowners bill, and is simple. The issue that you run into with this, is that you're still stuck with your standard deductible, which is often $500+.
3. Most insurance companies have a third option available, which is called a "Valuable Property Policy" (or similar verbiage). This is a stand alone policy. The benefit is that it tends to be cheaper, and has a much lower deductible (around $50). The downside is that it can often require an assessor to come value your collection, but that depends on your insurance company.
I chose option 3 for my guns. I have 20-25 guns at a given time and the cost is around $200 a year, with a $50 deductible. That's not bad at all. There are options, I'd recommend talking to your local agent before going to one of the online companies.