Business inkjet printer

I'm looking for a business inkjet printer made to print at least 7000 prints per month (10-20k would be better), I now have an HP K550 but after 2 failed printheads after 20K prints, they are rated for over 41,000 prints, I shouldn't even have used half of each head and already had 2 heads fail, although it may be in part due to my continuous ink modification, reviews of the K550 seem to suggest premature death of printheads is a very common issue, so it may not be my modification, I've done the same mod on an older HP business printer with 80,000 prints, a few liters of ink and no problems at all due to the mod.

I'm going to go buy antoher K550 now to finish my print jobs, but I may be returning it to look for a better model.

I have seen mostruous inkjets by Ricoh that seemed perfect... until I saw the $4000 US price tag. I'd like an inkjet with these features:
-rated for at least 7000 prints/month
-no "features" to prevent using refilled cartridges or continuous ink systems (I never buy cartridges and never will)
-user replaceable printhead
-ideally below $500, but will pay more if it's worth it
-fast speed
-Preferably large in/out-put trays (I do 500-1000 page print jobs or more, having to empty/refill every 100 pages is not fun)

Can anyone suggest an business inkjet that meets these requirements?

I'm trying to look at the Ricoh website, I had never even heard of Ricoh printers, they seem to have good business inkjets but their website mixes lasers and inkjets making it impossible to know which model is ink and with is laser.

Please do not recommend a laser - the toner cost is absolutely ridiculous - for $100 of ink I get the equivalent of $10,000-$15,000 worth of toner! I wouldn't even be able to keep my printing business running at the prices I have if I switched to laser (I do 500 double sided prints for less than $35 on my modded HP inkjets, have not had any complaints at all in 100k prints sold, only compliments on the good quality, and even at $35 I make a very high profit, I could sell it half that and still make a profit, with laser, I'd have to multiply my price by almost 10 to barely break even! So needless to say my printing business wouldn't work at all if I owned a laser printer).

Thanks