They are worth exactly what someone is willing to pay for them. Sorry if that sounds a little simplistic, but you have to have a market. No market = no value.

And the market for "used" shrubs is extremely quixotic. If you happen to find a landscaper who is doing an install that calls for something of this size and maturity, you might just have a deal. It is unlikely that you will find someone to take them off your hands for $$ just in case they may be useful down the road. If it was a 60 y.o. Japanese maple, your odds would be better, but personally, you'd have to pay me to haul boxwoods away. And generally, retail or wholesale nurseries only buy from licensed growers. Not always, but the better ones do and most retailers are restricted as to who they can buy from for disease and pest control purposes.

A shrub that large would require a rootball approx. 3' deep and 5' wide. The weight would be approx 800 lbs. or more. Normally a tree spade is used in order to keep the root mass intact and put into a basket.

Evergreen specimens of that size should only be transplanted when dormant, and when they can be immediately replanted. Otherwise the stress will most likely kill the plant.

ward33,
I'm going to make two assumptions, one is that you have English Box sometimes called 'Suffructicosa' and the other is that you have the expertise and equipment to dig, load,
and transport a massive shrub measuring 6'X 10'.
The value of the plants is in the digging and handling, also, will you guarantee survival? How do you replace it if one dies?
In my area there are brokers who specialize in handling large plant material. Contrary to previous post am not familiar with tree spade which can dig 10' wide shrub. Never seen a basket that wide.
Cutleaf Palmatums, Hinoki Cypress, and other high value plants of this size are hand-dug, drum-laced and loaded and unloaded often by crane. It really depends on how much money your client wants to spend.
Sam

You could calculate the value of a field grown boxwood of the size you have, based on how prices are calculated by reputable nurseries in your region (e.g. cost of growing + nursery overhead + percentage markup = price). Cost of growing can include cost of the original seedling, soil prep, fertilizers and any pesticides, water/irrigation, labor and a host of other factors.

The other possibility is attempting to interest the owner or head gardener of an estate or owners of a new "McMansion" who want the look of "instant age" for their landscape. You I'd get a solid estimate for the moving-placement cost so you could inform potential buyers of that expense. You need to consider whether you will arrange for delivery and installation, or expect the buyers to handle it.

As others already stated, the value of a plant is in the eyes of the potential buyer. Posting an ad with your asking price will tell you quickly whether there is interest. Sometimes, you'll see ads that say "$XXX or b.o." or "Make an offer." If you are flexible for negotiation, you could bargain with a potential buyer and eventually settle on a price that both of you think is fair.

Ward, all I can say is good luck.

I've transplanted 15 year old boxwoods that were about 5' x 5', and it was a bear of a job.

As others have pointed out a shrub that size needs a large rootball to be moved with it and that will weigh several hundred pounds. Plus if everything isn't right with the move and the new location the poor thing might very well die.

Not a project to be taken lightly.