Hello Overrun, welcome to the forum. First where roughly are you located?? That price for coal has to be for Bituminous coal..that is SOFT coal.. Anthracite coal which is HARD coal is a very different animal. So I suspect you are in western NY, western Pa, West Virgina, Eastern Ohio, or somewhere near the Bituminous coal sources..
Finding a source for coal is important, and which coal is very important. Bituminous coal can be added to a wood fire, it will usually burn completly or close to completely,, but if you add anthracite to a wood fire, just a couple of pieces, it will just sit there.. Even if you add a several inch-thick layer of anthracite coal over a hot wood fire,, if the firebox is not designed to burn anthracite,, the fire will just go out..
As for OWBoilers.. they are for the most part very inefficient.. regardless of the claims.. they are about 35-50% at best.. the rest of the heat from the wood goes up the chimney. A good coal boiler is around 75-85% efficient.. you can put your hand on the chimney pipe with most models.. there is that little lost heat going up the chimney.
I would recommend building a shed, with a masonry chimney, and installing a good coal/wood boiler.. Depending on the size of your house, and BTU needs, there are several very good coal/wood boilers.. Harman makes three sizes.. http://www.harmanstoves.com
[I think that is right] . This way you could make use of your supplies of wood, and still efficiently burn coal.. And like state in an above post,, most folks, once they burn coal, don't go back to wood...
However, if you truely ARE 'Overunwithsons' then the work of cutting, splitting, stacking wood, and keeping a wood boiler stoked can be a positive Famly-Time function.. and that is a GOOD thing...
The problem with OWBs is that they try to be selfcontained,, a small weather-resistant shed fitted around a boiler. with a very short chimney, a HUGE firebox to make up for the shortcomings of burning wood, and then the resulting smoldling fire, with lots of smoke.. Don't forget, smoke is unburnt wood, all that lost BTU's going away in the wind.
The best way to burn wood is very hot, and completely,, look into 'reverse gassification boilers' or gassification boilers.. http://www.hearth.com
I think is the premier site for burning wood.. But these boiler will not burn coal..
I started with an existing outdoor building, burried pex pipes, added a small wood/coal boiler.. notice I didn't type coal/wood.. I typed wood/coal.. the boiler was way too small, so I tried coal.. it was a little bit better.. stil to small.. So I copied the best ideas off the OWB sites and built a very good wood/coal boiler,, all 409 stainless, 2500# of 409SSteel !! and burnt wood in it for only a month or so before I realized it needed feeding every 4 hours, even tough it has a huge firebox... So I started burning coal.. I managed to learn from this forum, and experiment, and modify, and do it again, and again, and finally was able to have a fairly good wood/coal experience with my own boiler..
Then I bought a Coal-only boiler and rebuilt it, and am burning exclusively anthracite coal, and I just about can forget about the boiler for several days at a time.. it is bliss !! I burn about 1/4 the dollars in coal compared to Propane, and I keep the thermostats where I'm warm,, and comfortable,, I never was able to do that with propane..
There are few if any OWBs that will burn anthracite at all much less burn it well.. I'd go with an outbuilding, You will have an 'indoors' to load the fuel into the stove, and an 'indoors' to store some wood out of the weather,, where it can melt off the snow/ice from the woodpile, and you can store some coal as well...
My fingers are tired,, Hope the above helps.. I'm trying to not be too discouraging,, but OWBs were a 'quick and dirty' solution, now it the time to go with something more sophistcated, and efficient.