XPontus: Doesn't quite meet 100% but probably as close as you'll get without shelling out currently; and OS so could be extended at some point to fully match. Certainly does match that cheaper - since it is free.
- XML grid view: hmm not 100% sure what you mean by that but I there is a tree view which I think is what you're meaning (I have limited experience with XML though I'm learning a lot - Revenue Canada has great resources actually)
- generate XML data from XSD files and vise-versa: Can generate schemas (of a few different kinds: DTDS, XML schemas, and Relax NG grammars) from XML documents. See screenie below for the New from Template option options.
- check XML files for validity and being well-formed: Has a validity checker.
- load very big XML files really fast: I don't have any that I'd call big so can't comment on this (pretty much instant for 1500 line xml files on my HP Intel i7 2gb Ram Laptop)
- Of course all common features...: mostly - specifically missing: Search in files.
No Bonus Points: Doesn't generate C (or any other) source code.