@TonyFF
I think you will be disappointed by how expensive they are! :-) My guess at least 500 euros /m2 for basic options, probably more these days.
Prefabs are quick and easy, so they do have some advantages. You lay a concrete base, and they just come and plonk it on top. :-) But... our house is in a lovely (and popular) village in the Balkan Mountains, and I keep a careful eye on what's done there as I think Bulgarians do know best! :-) Almost every house in the village has been renovated over the last few years, so most folks believe the most economical option is to upgrade the standard village house (uPVC double-glazing, external and/or internal insulation, to start). I saw a couple which I thought were way too far gone to be saved, but, nope, they're both very nice houses now (one of them put in gas-fired central heating with a propane tank buried in the garden). You save the cost of knocking it down, the hassle of planning permission, and you can live in it while you renovate it over the next 1-50 years. :-)
There are maybe 20-30 brand new houses where the old house was knocked down first, but these are all large and rather fancy properties with standard concrete construction (base/pillars, brick in-fill, tile roof). There are just 2 prefabs. My neighbour's place (a big DIY project that I discuss below), and a very big and very nice wooden house (American log-cabin style). Basically a prefab/kit, as I watched them truck the panels/bits in and then assemble them.
I looked at prefabs from China (AliBaba, etc.) and the cost looks very appealing. However, I didn't buy one as I'm concerned about the extra costs (shipping, local transport/installation, duties/VAT, and upgrades from the base price, etc.) and whether it would really be competitive. But it's certainly worth a look to see what you think of them.
Instead, we built a small cabin, using prefab-style construction (i.e. concrete base, steel frame, SIPs). So far, it has cost well over 20k euros (for 25 m2 ish). And we soon realized we didn't have thick enough insulation, which would have cost significantly more. We subsequently did a 2nd stage with another thick panel on the roof in order to have more insulation (better, but still not great) and create a covered veranda which will become a large living room and almost double the space. This will bring the cost/m2 down a lot, and with a wood-burner it might make the whole thing a bit more livable in winter. It's actually not a bad DIY effort, but it looks very much like a basic prefab with standard white SIPs.
To just buy a prefab ready to go, I see tophouse advertising everywhere, so you could look at them. I also have a friend in Plovdiv (Anton, good guy) who has been importing them from Turkey (cheaper than Bulgaria) for many years. He has two ranges, one which looks kinda prefab, and a more fancy one (more expensive, of course) that looks like a standard house. He put the latter option in on his own plot in a village outside Plovdiv, and it looks very nice. I doubt it was less than 1k euros per m2 though.
His company is homeskisiov and he has a website and he shows up on Google search (with great feedback and plenty of external/internal photos). I've seen his house, and it's on Google Street View, so if you PM me I can share his contact details and his house view.
My neighbour (that @janemulberry mentioned) is the borehole master of Stara Zagora (and elsewhere). He's a very organized and capable guy, and I like him a lot. He agrees with you, and thinks that village houses should be torn down rather than renovated. He did exactly this not far from my house. He then built a huge house himself, using the same basic prefab construction I mention. But his is not a 25 m2 cabin, it's a 250 m2 mini-mansion! :-)
It's still basically a big box with a large concrete base, a steel frame, and SIPs for the walls and roof. He has floor-to-ceiling windows across the front, but minimal openings at back/sides. He used very thick panels (for cold Bulgarian winters and hot Bulgarian summers), and he put fancy cladding on the front and roof so it looks good. He also put in under-floor heating using water from a ground-source heat pump (i.e. down one his own boreholes), together with solar hot water and solar panels on the roof. It looks fab, I gotta say, and I'm sure it costs pennies to heat/cool. I doubt he would build to order, this is more as an inspiration if you fancy a bit of DIY to build something similar. His house is also on a road visited recently by Google Street View, so I can also share the view of this prefab gem. :-)
