We can do some "back of the envelope" calculations based on Leto's conversations with Hawat. Note that these figures are very rough and contain a considerable number of assumptions:
“They neglect to mention that less than half the crawlers are
operable, that only about a third have carryalls to fly them to spice
sands—that everything the Harkonnens left us is ready to break down
and fall apart. We’ll be lucky to get half the equipment into
operation and luckier yet if a fourth of it’s still working six months
“Pretty much as we expected,” Leto said. “What’s the firm estimate on
basic equipment?” Hawat glanced at his folder. “About nine hundred and
thirty harvester-factories that can be sent out in a few days. About
sixty-two hundred and fifty ornithopters for survey, scouting, and
weather observation … carryalls, a little under a thousand.”
The Duke turned to Hawat. “Thufir, did you get those account books you said you could buy?”
“Yes, my Lord. They’re being examined in detail even now. I’ve skimmed them, though, and can give a first approximation.”
“Give it, then.”
“The Harkonnens took ten billion solaris out of here every three hundred and thirty Standard days.”
So, with about 1500(ish) operable spice harvesters, the Harkonnen were able to extract around 6.6M Solaris per annum per harvester. A single load seems to take a day or so to harvest and let's say a day on either side for repair and recovery so each harvester can make maybe 100 trips a year. That means that each single load equals approximately 60,000 Solaris. and that, assuming it takes a year to replace, results in a total loss to the business of over 6,000,000 Solaris as well as the value of the harvester itself (h/t to @friggle for pointing this out).
But we can go further....
Since we know that the price of spice can be as much as...
620,000 solaris the decagram.
...we can estimate that a full harvest load might contain as many as 10 grams of refined spice.
As the average suitcase can hold 20000 grams, you'd need some 2000 trips to fill one.
Since the 1500 harvesters can make approximately 150,000 trips per annum, that means that a suitcase of spice (with which one could purchase a planet) is worth around 10-15M solaris or roughly twice the average annual output of a single harvester.