Well, de gustibus non est disputandum and all that.

(I will say that, this being GW, "it's going to be cheaper" was never something they put on the table, though.

)
One of the nice things about it is that there are still rules for everything - for free even. You can get all the Old World unit stats
here, and points on the warscroll builder
here, which is plenty (along with the likewise-free core rules) to get models on the table - I'm actually surprised, as I look into it, as 40K doesn't give nearly that much free support. The only thing you miss is army-wide special rules, of which there aren't a lot (with the notable exception of armies heavy on summoning) as every unit's warscroll has all the special rules that apply to it right on it.
Heck, even in the month or so I've been looking into the game, I've seen people bringing Bretonnians to tournaments, and doing well with them no less. Lots of room to use your WHFB armies.