I saw a couple of MR 2005s on eBay last night for 200 or less as buy it now. Also saw an auction that was at 90 with 11 hours left as of last night.
The RomFX Revo is an option many use, but they are pricey. The multi-stomp can work too, but I don't have experience with it.
I have a CP cape, robe and custom 2 piece body suit. The pricing you're receiving seems about right. At least one of our Vader's had a custom cape made and I think it was local (DymnDog). I am not sure what price difference you would see going that route.
Vader just isn't a cheap costume, especially to make it look great.