I kind of get it. Though you have a lot of options here.
I would do one of two things:
1st: a warboss with big choppa, bosspole, and Armour
With a squad of 30 sluggas with nob with pk
And a mob of 20 shoota boyz with nob with bosspole and 2 special weapons in the squad
Finally a unit of 10 Grots this should come to 499
2nd: (and my favorite)
The same boss from above
Although with 11 sluggas and the pk nob in a trukk with a boarding plank red paint job and ram
A second trukk equipped the same with 12 boyz and the nob as above
And finally a unit of 2 skorch-trakks
The second option is faster and is a threat sooner which is why I like it for your list
I would do one of two things:
1st: a warboss with big choppa, bosspole, and Armour
With a squad of 30 sluggas with nob with pk
And a mob of 20 shoota boyz with nob with bosspole and 2 special weapons in the squad
Finally a unit of 10 Grots this should come to 499
2nd: (and my favorite)
The same boss from above
Although with 11 sluggas and the pk nob in a trukk with a boarding plank red paint job and ram
A second trukk equipped the same with 12 boyz and the nob as above
And finally a unit of 2 skorch-trakks
The second option is faster and is a threat sooner which is why I like it for your list
