You could ask for flat rate $150 lower 48 states and then if they're close by simply refund the difference or invoice (if they haven't paid yet) them for the actual shipping costs. I'm not sure if eBay allows for shipping costs to be determined at the end of the auction. If they do, you can state that in the auction description. UPS stores charge extra over what UPS charges to ship, in other words, they get a profit above the normally reasonable UPS ground rates. Then they add costs to pack the boxes. So if you go UPS pack yourself and have them pickup the box at your door.
The more you nest the drums (with adequate padding between them inside to protect them) the better the shipping rate will be; however this also involves more personal time spent packing them. I usually use Fedex home delivery after packing myself, but I'm experienced in doing so. Also keep in mind the box dimensions are always part of the equation in determining the cost of the box, so the bass drum will need to be economically-yet-effectively packed. It is difficult to find a bag that a bass drum fits in, but if you get some foam padding sheeting or other thin protective material, you should be able to wrap it well.. Also make sure the items in the box DO NOT SHIFT in the box when you shake the box, as in transit they almost NEVER end up on the right side, and there will be several opportunities for the box to sustain drops (in fact, UPS suggests the box be packed such that it can sustain a 5 ft drop!)
All this being said, if you still want a pro to pack for you and have the buyer pay for it, state such up front: Just be ready to accept a slightly lower amount for the drums because buyers are going to bid accordingly.