Rapha, nice but a bit pricey?

Buy short sleeve base layers and merino armwarmers from Planet X for £5 to use as baselayer.

I've just ordered a pair of the armwarmers. Let's hope they're nice but not pricey.

They are identical to Endura Baa Baa and will last for ages as long as you take care with the seam at the cuff when pulling them on/off over a watch. Which I'm not.

I've just been out in these £5 merino armwarmers...

They're very comfortable and long enough (in XL). Obviously not windproof as some arm warmers but a bargain and will be perfect as a mid-layer.