Excessive
Nobz are a bit excessive at the 500 point level, but not impossible. If you're going to use one, however, you should include a warboss, not a wyrdboy. That way, you can take the group of nobz as a troop choice, rather than an elite, leaving only a single troop slot to fill.
Also, those nobz need to be in a trukk, or they are going to be shot to pieces long before they reach close combat. I understand that trukks can be expensive, but you could look on ebay and probably get an older trukk for $10-15 rather than the $30 retail cost for new ones.
That mob of boyz also either needs a nob with a powerklaw, or it needs to go. Frankly, you could probably let it go.
Here's the way I'd run the army:
Warboss w/powerklaw + 'eavy armor (90)
6 Nobz w/2 powerklaws + 'eavy armor + trukk + bosspole (228)
20 ork shoota boyz w/2 rokkits + Nob w/powerklaw and bosspole (180)
The Warboss starts either attached to the nobz in the trukk, or the team of shoota boyz, depending on the situation.
Now that's a mean 500 point army. It's only two units, granted, but as long as your large force keeps their attention away from the trukk (which should be kept out of sight until it reaches close combat) it's more CC power than most 500 point armies can handle. Having shoota boyz in the footslogging mob gives you back up fire support. You might also want to consider upgrading one of the nobz to a painboy, but I don't have those rules with me, so I don't know how it'd fit with your costs.
If you'd rather take a wyrdboy, and go footslogging instead, then upgrade him to a Warp 'ead (this is very important), and drop the nobz. They're going to be shot to pieces if they don't have a transport.
Here's that version:
Warp 'ead (85)
22 shoota boyz w/2 rokkits and nob w/PK and bosspole (192)
21 slugga boyz w/2 rokkits and nob w/PK and bosspole (186)
Rokkit buggy (35)
Attach the wyrdboyz to the slugga boyz, sneak the rokkit buggy around to attack the enemy's vulnerable side, begin the march and have fun.
