I disclaim this post with the following: I run a single daemon prince in my daemonzilla lists.
Some may disagree, but Soulgrinders are very good matches for the daemonzilla style list: they laugh heartily at S6 and under (where's your multi and scatter laser spam now?), and still handle ludicrous amounts of non-melta shots due to possession. Plus soulgrinders fill a problematic area for daemonzilla, ork hordes. Ask an
IG player (if you can find one) what a leman russ will do to a 30 boy mob. That's right, gut it like a fish. Unlike the russ, the grinder gets to throw out 6 bolter shots and then assault as well. Oh, and the
PK Nob? S9 hitting on 3+ is no major concern,
tbh.
Anyway, back to the daemon princes.
For example, this is how I generally outfit mine:
Daemon Prince
Iron Hide (mandatory)
Mark of Nurgle (get this, unless you need a specific power from another mark)
Cloud of Flies (5 pt
def/off grenades? yep, you guessed it. manditory w/
MoN)
Noxious Touch (rerolled 2+ to wound against everyone but other
MCs, who're just 2+ wound? lmaonaise, I say.)
This guy'll run you 150 points, which is dirt cheap for what you get. You can give him things like breath of chaos, which is pricey but'll make a pack of terminators weep. Daemonic Gaze is also good, relatively inexpensive, and gets maximum use out of the prince's BS5. I usually attach gaze to my princes, giving them some respectable ranged threat on the charge in. It suckers poor saps into wasting time trying to kill them, too, which I love.
Something to keep in mind about Daemon Princes: I find Nurgle
DPs have one primary job, and that's to stand in front of shooty units and wave their arms and shout, "Shoot me! Shoot me! Ignore the big red guy cutting your Land Raider into steel ribbons, I'm menacing your gunline! GRRRRRR!" WS6 T5 4W 3+/5++ and defensive grenades for 150 points. Mee-yow. I've had my
DP soak both a 30 boy and 12 genestealer charge before (seperate games mind you

). You can kit them differently, and they mash marines like crazy, but they generally lack the attacks to be truly killy vs. rank and file troops.
One other thing you might want to consider, and I have a very hard time hitting the table without them these days, is a suicide flamer squad (3 flamers of tzeentch, for 105 points). I tend to employ them as a 105 point cruise missile of doom. I've wiped 6-man terminator squads, 15-strong loota squads, crippled 30 boy mobs and biker nobz, even immobilized a land raider or two. These guys are like my ace in the hole, I pull them out and blast them at whatever most needs removal. Either bring them in off an icon to bail out a scoring troop unit, or drop them in the backfield on some unsuspecting sap and watch whatever you shoot wither and die. The more expensive, heavily armed and armoured unit you can find, the better.
So, yeah. Soul Grinders, Plaguebearers, and Flamers. Give them some thought, see if they're right for you and the way you play this list.
And for those who're wondering about the weak linch pin of this army? It's the wallet of it's general

Bloodcrushers are exorbitantly expensive, and the only reason I don't run true daemonzilla lists (I have to satiate myself with 5 crushers, 3
MCs and 2 soul grinders.)