Orks don't really suffer from lack of low-
ap weaponry. Orks counter quality with quantity. Oh, this fancy gun can evaporise a marine! Guess what, an ork boy is gona die as easilly as a space marine but costs 2.5 times less. And in the anti-tank department we have cheap rokkits that can be massed.
But building a strong ork army is tricky. You need to focus on a theme. Here's something about the orks.
Depends on what you really want to get. Is it Chaos main and orks allies? If yes, than i'd probably stick to big gunz or tankbustas in a wagon. They're a steal for the points. But most other stuff like boyz and bikers require support to work properly. Namely, a biker blob needs a painboss + warboss and than they're gona wreck faces. And same with wagonboyz. But without either of theese - not too much.
Orks are not really great when taken out of the context.
But if you're running orks as main and
CSM as allies, than you have much more options. Lord/Sorc + Spawns/Bikers work really great with speed freaks. Landraider with something choppy inside will fit in a wagon rush theme better than anything covering the wagon'z sides with it's mighty av14! Obliterators are alwayz handy. Murderpack for a kanz wall!