Spider based ones from Sigeyi get decent reviews and are not much more than that. Some may be nervous about buying from China but my Magene one is pretty accurate and has been trouble free
They seem to be advertising in the UK and Europe now and have put their prices up accordingly but still probably not a bad shout. I wouldn't be scared away by chinese ones but I would like to use my shimano cranks primarily. Second choice would be to pick up some rotors or Sram and use the Sigeyi
I've got a Magene Ultegra R8000 (dual sided rather than just one crank arm) PM but it doesn't look like they sell the single-sided crank arm option any more.
Don't know what BB system you're using but I've got a set of Rotor 3d24 cranks with a p2m (pizza slice edition) which I'd pass on for £200. Used condition and the chainrings are brand new. Can send pics if you want
Spider based ones from Sigeyi get decent reviews and are not much more than that. Some may be nervous about buying from China but my Magene one is pretty accurate and has been trouble free