Cheapest way to ship large speakers?

Freight. Pack the speakers individually. Get a correctly sized pallet and strap them down laying side by side with extra layers of protection to reduce the chance of a fork lift damaging them. I had some speakers shipped to me that were about as you describe from Chicago to Calif. for 3 or 4 hundred.

I would not ship them unless they were packed in their original box with the original packing material. Any other way you'll be asking for trouble.

I'd also say freightquote.com. I've used them without issues and you can choose the least expensive of the quotes.

With Fedex and UPS, you run into "dimensional weight", which may be 3 cubic feet or some maximum height (40"?) and can easily double the costs. Found that DHL is easier and cheaper on bigger packages. Although, not sure how cooperative it is on the receiving end for home delivery. Couldn't be any worse than Fedex.

a $1000 to ship? I hope you you aren't shipping them to Nigeria