I am going to make some suggestions of which several of these are going to be geared a bit more for Krenko, Mob Boss as I still don't know what your commander option intentions are. Chromaticus' suggestions are good and cheap so I will just tag some suggestions onto the back of those also being good.
Goblin Chieftain - Giving Kranko haste is huge. GIving his new swarm of goblin tokens haste and buffing them to be twice is big is also kind of huge. I think this does a lot for Krenko and it might in my opinion be the best pickup for the money for that specific commander.
Goblin Warchief - I think that the anthem of
Goblin Chieftain is better than the cost reduction here but I think both are really great.
Goblin Trashmaster - Its an anthem but the big take away is the ability to smash a bunch of things on demand.
Goblin Lookout - Its cheap $$$ to pick up and its a good anthem if you go super wide with a commander like Krenko.
Goblin Matron - It adds to your goblin count and goes and gets a friend.
Pashalik Mons - It can help as a little bit of a buffer against sweepers. His token gen is bad but his on death trigger is a fairly decent punish for sweeping or blocking.
Legion Warboss - Tokens
Siege-Gang Commander - Tokens
Gempalm Incinerator - Cheap answer that also cantrips. Its nice to have when in the tribe and given how wide you ideally go its a solid answer.
Goblin Instigator - Budget Tokens
Mogg War Marshal - Budget Tokens
Beetleback Chief - Budget Tokens
Hordeling Outburst - Budget Tokens
Krenko's Command - Budget Tokens
Dragon Fodder - Budget Tokens
You See a Pair of Goblins - Budget Tokens
Goblin War Party - Budget Tokens
Goblin Rally - Budget Tokens
Swarming Goblins - Budget Tokens
Some non goblin cards that I think suppliment this idea well:
In the Web of War - An outlet for haste as well as pumping the token army.
Ogre Battledriver - Its a cheaper money and mana version of
In the Web of War that has the downside of being on a non goblin creature rather than an enchantment.
Shared Animosity - Its a little pricy for your budget but a strong finisher for red when working with big waves of tokens.
Tears of Rage - Its sort of the budget brother of
Shared Animosity.
Impact Tremors - non goblin finisher option. It bypasses needing to use combat which has its advantages.
Skullclamp - Expensive for the budget you outlined but its great draw when dealing with a bunch of chaff tokens.