my two cents, and mind you this is just me.

I wouldn't wear an Eton jacket with a four-in-hand tie. That's a "regular" tie. An Eton is basically a tailcoat without tails. Think: tuxedo. I only wear my eton with the formal shirt and bowtie.

If you're hurting for a daywear or less formal jacket and have to pinch pennies until they squeal, hunt the thrift stores and find a nice tweed or camels hair sportcoat and modify it. I just got a wonderful gray camels hair jacket from the local Goodwill shop for $20. Now that I've paid attention to David Dalgliesh's and the F-H.C.A.G's threads on jacket modification, and I know what I don't like about my tweed modified jacket, my second attempt will likely be better than my first kilt jacket mod.