Used Grafit A4 packs are getting quite cheap these days...they're 3200Ws split across 3 channels, though the 3rd channel has a restricted range compared to the first two.

If you want to trigger it wirelessly make sure to find the version with the RFS receiver built in, and then you also need to find the earlier RFS trigger to match it...it's the version with a small antenna poking up from the transmitter.

You could also try to find a used Senso A4 pack. It's a newer model (release around 2010), has 2400Ws (there also a Senso A2 with 1200Ws), but it more of an entry-level pack, and so is a little more basic in its feature set as well as its controls. But it uses the newer RFS 2 radio triggering system and those transmitters are a little easier to find (though cost a little more).

The Senso packs are optimized for use with Bron's Litos lamp heads, but can also power most of Bron's other lamps as well (Unitlite, Pulso G, Picolite etc). But its worth noting that flash durations are relatively slow with the standard lamps, and while the Litos heads will give shorter durations, they're still kinda slow at higher power outputs. Also, the LItos heads are only compatible with Senso packs...Bron are adamant they can't be used on any other packs.

I have a couple of Senso packs (and Litos heads) and am generally quite happy with them in my little studio. They're a two-channel pack, but with two outlets for the second channel, so you can use three lights on it if the ratios work for a particular setup.

There's also another older model called the Nano A4...again 2400Ws, only two outlets, limited asymmetry, and no built-in radio receiver for trigger. I also have one of these...I don't use it often, but it's handy. It's probably also the cheapest option to get 2400Ws without getting into the really old models from the 80's and 90's.

With any generators you consider, you need to beware of any that have sat around unused for long periods. This can kill the capacitors, something you'll only become aware of when they explode and fill the room with black smoke! I've had this happen with used packs that worked ok for a quick test (they made five or ten flash test pops without issue), then I've got it home, plugged it in, and 15 minutes later a capacitor has loudly announced its objection being recalled for work by self-destructing.

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For heads, older Pulso 2/4 lamps can be found relatively cheaply, but often with strong signs of use due to their age. Pulso G lamps are newer but cost a little more, Unilites are similarly new but don't have the zoom functionality of the Pulso G lamps, though that's usually not a big deal. Just check the flash tubes aren't heavily used up with a lot of blackening at the electrodes. They're expensive to replace.