There's a few of them that I've used that are probably cheaper per edge than what you're using now. Ingersoll Gold Trio comes to mind, Iscar H690, Seco Square Six.
If you're doing a lot of the same parts, like material, like set-ups, square six will outperform (and also likely be cheaper per edge) the other two in my opinion. Two downfalls though: 1). It doesn't like ramping. 2). The inserts are ground so they must be matched up - so corners 1-3 on each side need to be indexed to match all the flutes. I mean, you can get a killer finish with it, but if the machinists/operators are scatterbrained that can go sideways on you quick.
Seco doesn't run a lot of promos with deep discounts like the other companies though. Iscar might throw some free stuff at you, even Ingersoll with a good rep might do the same. I've seen that there's rarely a cheap way to get into Seco milling tools, but when you do get into them they're worth it.
Someone else mentioned Mitsubishi. Can't say enough good about this company, assuming you'd get a good rep. Great technical support, super affordable to get into their tooling, and really good to work with if something unfortunate happens with their tool when you're using it.
Either way make sure you call up some reps and test them out before you buy anything...see what kind of deals you can get and get an idea of how the support is in your area. Some of the tool guys don't know shit about what they're selling.