For cymbals going long distances I've gotten much better rates via Reverb "shipping" choices that I could get on my own. Sometimes it's UPS or other times it's USPS. At times up to a $10-$15 difference either way. Since you're already doing Paypal, you'll still have to pay the 3% Reverb fee. But since that's only $3 out of $100 it's often a bargain to list on Reverb and get better overall protection (for both buyer and seller) rather than doing it alone. If you're shipping to one of the 10-12 states that Reverb now collects sales tax for, then that probably kills the any possible advantage to the preferred shipping rates Reverb can usually get. One downside with the Reverb shipping is that you cannot find out the preferred rates until you have an order in hand to buy the cymbal - and the buyer has paid. It will be less, you just don't know how much less. You also get charged less for a delivery signature (usually required by Reverb) and the insurance is cheaper. A better deal all around from my experiences.
You can go on line for USPS postal calculator or UPS package estimator with package weight and dimensions to get a very close estimate. When I've gotten a FedEx quote on line the store I bring it to usually adds approx 15% for their expenses/profit. When I go it alone I usually find USPS to be the same or cheaper than FedEx or UPS....but I don't have accounts with them. Does it cost anything to set up an account with the other shippers? Is there a certain volume required to get or keep a "preferred rate" account? Greyhound bus package express is probably the cheapest of all of them, especially for large items. Some members have good luck shipping drum kits for 1/2 to 1/3 the price of other shippers.....much slower though.
Sign up for a UPS account online. Use the Promo code "BETTER."
As mentioned above, use a bi3x 24x24x4.
You can get a 24 cube at uhaul and cut it down.
Post office and UPS stores will be much more expensive.
It depends on size, weight & distance. Anything largish, heavyish, and more than one state away will almost always be cheapest with Fedex (I've priced UPS, USPS, & FedEx shipping $ for the same item many times).
22" cymbal, 24 x 24 x 3" box, no larger, well padded (I use pipe insulation & air pillows). Seriously, volume counts for as much as weight with all the major shippers, USPS finally having gone with dimensional pricing only a couple months ago.
Having an account at Fedex will get you a discount on each shipment (I assume because they have potential recourse in case the estimated charge turns out under, e.g. residential instead of commercial destination).
They also have month-long $5 off coupons a few times a year, but in that case you wouldn't use the shipping account and pay cash instead.
Perhaps not the cheapest but when I was shipping Bettis cymbals I used USPS and would avoid shipping ground, when for a dollar or two more it would go priority air. Less handling and delivery in 2-3 days instead of 5-7. I shipped hundreds of cymbals and never payed for insurance. (priority includes $50). They never screwed up...not once.