Millarkie - we have an Extraflame Lucrezia Idro. You can download an info sheet on the entire Extraflame range from here (PDF). This is not the supplier we used though.
We replaced an open coal fire with back boiler and our annual fuel cost is currently projected to be about £800, down from about £1,200. Our house is wood, with poorly insulated walls, although it has new double glazing and loft insulation to current standards.
Depending on your supplier, you would get your fuel for about £2.20 per 10Kg bag of 6mm diameter pellets, provided you are buying at least one tonne at a time (i.e. 100 bags). Our heat requirements mean we get though 2 bags per day, or about one bag per six hours of continuous use. Unless it is especially cold outside we have the power output of the stove set very low. If it is especially chilly we turn it up - our house does not retain heat at all well.
Biomass stoves are not as controllable as gas or oil. Timing them is a bit of an artform. We have learned that we need to have it set to come on at the very least one hour before we get up in the morning. The heat goes to the cylinder first, then to the radiators once the cylinder is up to temp. This takes about 40 minutes. Once the heat gets to the rads, your house will warm up as quickly as it does with your current system.
When the system switches off, it has to burn up the wood remaining in the burn pot, then continue to circulate water to the radiators until the stove has cooled sufficiently, so it the radiators will still be hot for almost half an hour after you ask the system to shut down. A little more foresight is therefore required, but once you're used to it it's no problem. Just to add to that, you would find it would run more efficiently if set to go for a long period at low power rather than switching it on and off all the time, which it sounds like is what you're doing at the moment with your oil.
I would say based on my research that the cost comparison with oil is already favourable - just - and is only going to become more so. I know a few people round here who are thinking about what to do when their current oil boilers reach the end of their lives, and none of them wants to buy a new oil system.
If you have a large house with a big demand for heat, you need a larger boiler with a much larger, self-feeding hopper. Ours holds 45kg and we top it up every evening. If you get yourself one of these Okofen babies, then you can put an entire winter's supply of fuel in it in one go and forget about it. You need a sizeable garage or outbuilding for it though.
Even with the Lucrezia system you need somewhere you can store at least a tonne of pellets - we built a new shed, which has a 3x2m floor area, and one half of it is stacked to the roof with a little over a tonne.
On the subject of solar panels, you can't use them to heat your radiators. They don't generate enough heat at the time of year you would need them to. Solar thermal panels dump their heat into a cylinder, where your hot water gets its heat from. The water in your radiators is, in most systems, heated directly by the boiler without going anywhere near the cylinder. You can get systems where everything is fed from a 'thermal heat store', so theoretically the solar panels would be contributing towards the radiators, however in such systems the thermal heat store is invariably huge and expensive - and the contribution from the panels in midwinter would still be modest at best.
Some more useful info on wood heating to be had here.