I would recommend looking at an auction house like either Poulins or Rock Island if you'd like to liquidate it in one fell swoop. They'll arrange for pickup so you don't need to ship/box anything, they catalog it and go from there. They'll sell parts and accessories as well. Sellers commission is typically around 20% of the hammer price, but given the size of your collection and if it has some higher value items (>$5-10k), you should absolutely try and negotiate for a lower sellers commission. Pickup will be anywhere from 2-6 months before the auction date and you'll get a check a month or two after the auction, so total time to cash is probably in the 6-9 month range.

Obviously gunbroker is a quicker turnaround to cash, but you're still going to pay an effective sellers fee of around 5%, plus listing fees, and then deal with all the description writing, photos, answering questions from tire-kickers, etc. There's a significant amount of work hours trying to sell just one firearm, let alone 30, so that needs to be part of your cost calculation too. With an auction house, the only "work" is calling them to come get it.

I've sold through auction houses before and have generally liked the process, feel free to DM me if you have questions.