I recently visited a yarn shop I hadn't been to before, and they had some different European lines of sock yarn that I immediately bought to try. Both have an excellent price point (less than $15 for a pair of socks).
1. Phildar Phil Folk 50 - this stuff is made in Romania but marketed through a French company.It's a 75/25 wool/nylon blend at 210m/50g. I'm pretty sure it's superwash although it doesn't say that on the ball band. It's a close match to Regia in terms of colour and fuzzy texture, and the colourways are nice and natural with lots of greys and browns to choose from. It knits up nicely and has reasonable stitch definition, although there are very slight variations in thickness in the yarn every once in a while. The brown colour I chose has a halo and a very slightly tweedy appearance. Excellent for casual men's socks. The socks do have a slight tendency to pill after repeated laundering (not as good as Regia on this front). I think this yarn works best for knit/purl designs; the twisted-stitch openwork I tried didn't work well with the yarn's halo.
[phil folk 50 in action]
**update 10/2016 **
I've now used grey phil folk 50, and it isn't as hairy as the brown colour. It's very close to the Regia. I like this stuff.
2. DGB Confetti superwash - made in Italy and marketed through a French-Canadian firm, another 75/25 wool/nylon blend at 210m/50g. This yarn has a very tight ply and has a nice "boing" factor as a result. It's soft - as in squishy - and has no halo. The tight ply gives it beautiful stitch definition, so it's prime for cablework! The socks turn out smooth and dressy. The colourways are not as "natural" as the Phil Folk 50, but there are reasonable solid colours on offer. I think there are also self-striping colourways. I've got a solid rust-red, a dark teal, and a hot pink. It's very nice to knit with and launders beautifully. The downside is those colours - if it's browns and greys you're after, you'll be hard pressed to find nice ones.
[DGB confetti superwash in Treppenviertel socks]