Still not a combo I'm actively searching for, just happens to crop up in 1/2 of games. People dont think its a threat until zombies are spawning as 6/6 minimum and by then its usually too late. Definitely something to develop further.
Still run zombie lords as the +1/+1 combo doesnt come off that frequently and I havnt worked out the best way to tutor for them as yet.
Only recently started working on this part as an adaptation to your zombie build - so do have evasion like Akroma's memorial, Filth, Craterhoof Behemoth. Also trying to find a way to do damage without alpha swinging so I'm not reliant on evasion - direct damage based on creatures power is something I'm looking at (dont think there is anything in BUG suite that Im familiar with).
The deck works well without self milling until you get the +1/+1 suite in play. Then you mill like made, generate a billion huge zombies (included Second Harvest for fun) and hope nobody is holding Cyclonic Rift.
It makes all zombie tokens ridiculously large when they hit the deck, also opens up the ability to mill your opponents to death as alternate win con with Altar of Dementia or Undead Alchemist, which is what happened last night (swung with regent for lethal at one opponent, added tokens, then sac to Altar to mill last opponent for 98).
I had planned to include Gary aka Gray Merchant of asphodel to ensure life total was greater than opponents. Cast Gary a few times in a turn and then tap Shepherd of Rot. Also good if the game is dragging on for ages and you want it to end...
Still looking in to options for the deck, most of the combos so far are pretty situational and it suffers from GY hate a lot - no Eldrazi for me!
Building my own zombie themed deck - staying with a budget a little less than your list however... Have you considered Shepherd of Rot. Coupled with Kiora's follower, etc, to untap a few times could give another easy alternate win con even if you only have a moderate number of zombies in play. Provided you're in front of course, which you typically will be with an aggressive deck.