I don't think you'll necessarily find it any cheaper to go for the 130r in the long run... I think it's difficult to quantify the cost per print. You've got a good budget (2.5k) to get a solid entry level designjet, personally i'd want one which is tailored to the job you want it to do.
Another one of my friend had a 110r, I'm going to assume it's similar to the 130. They didn't look after it tbh and I don't think it works any more... I'd rather have a floor standing one
If you're worried about cartridges then I'd look at the t610 (or whatever HP have since replaced it by). I've used it a lot and it's pretty impressive. It takes four cartridges IIRC. I think my housemate got hos for £12-1300 or so. Gives a lot left over for cartridges.
Either way, I don't think you can look at the figures and work out the print cost. It would be best to control what people are printing, i.e. my housemate charges people extra if they're printing black A1 sheets with white text on them. It might look great on screen but never prints well and uses up a ton of ink.
Maybe worth picking up a couple of cheap A3's to supplement the large format. Printing A3/4 on a designjet is a lot more expensive, and you're wasting a lot of paper on the roll if you do that.
I have a couple of A3 injets -
HP B9180 - awesome photo quality. But... printheads have broken, and it takes 8x£25 cartridges so not exactly budget.
Epson stylus office B1100 - Ok quality, better for documents etc. Only four cartridges so much cheaper. Enjoys chewing up paper.
Would probably be better to have an A3 laser to supplement a designjet...
edit: bear in mind these printers are supported long beyond their lifespan...