The cost difference was big. It's been a few years, so forgive me if I don't recall the exact numbers, but I'll do my best. Without hired help and buying all the supplies myself, I estimate my daily expenses for my mountain trips less than 20 USD (including everything except transportation to and from the trailheads). Staying in Huaraz was more expensive, among other things because I ate in the better restaurants in town, and often twice a day.
WIth hired help costs rise dramatically. Different agencies will quote slightly different prices, but in 2011 a normal price for fairly standard stuff was close to 100 USD per day, for a private guide for a solo climber. I think that that's what I paid for Chopicalqui, the 4 day trip for which I hired a guide. I hired porters several times, and a porter with glacier skills was 30 USD per day. I don't know the rate for a cook, but it must be less than a porter with glacier skills. So, going without a guide saves the 100 USD plus the cost of his food. If you don't hire a porter either (in the Ishinca valley you don't need one, and certainly not one with glacier skills) that saves another 30 USD plus food. And without them, you don't need to rent a tent for them to sleep in either - another few bucks saved.
Gear rental was cheap, but I rarely rented anything since I had everything myself. Only for Chopicalqui I hired a second tent and stove. However, renting a lot of stuff will probably add up. I'll leave it to others to estimate what you can save by bringing your own gear. Personally, if I could bring just one item, it would be my boots. Never mind the cost, but it saves me the time and trouble of finding a rental that fits properly, and I know that my own boots will keep my feet warm. Then again, when possible I prefer to bring not just one item but all of my gear, if only because I'm familiar with it.
My time commitment to buy all the supplies was just a couple of hours in the evening before, and another hour the next morning. However, as I said, I knew my way around town; otherwise I couldn't have managed that. Probably it would have cost me the better part of a day instead. More importantly, if I wouldn't have had experience in organizing my own climbs, I couldn't have managed that either, or might easily have forgotten something essential. For example, I met a couple of young women planning and organizing their own trek, with an arriero but without guide, and they sure appreciated it when I mentioned that, besides food, items such as matches and toilet paper might be rather handy...
But, as long as you know what you're doing, buying supplies yourself is the best way to ensure that you've got food that you like. And it's a bonus to watch the amazement on the faces of your porter and guide when you they see all the delicacies you've bought. I mean, I just bought food that I liked, even if some things were quite expensive for Peruvian standards. Sure, most things were cheap, but there were exceptions. Some things that are common to us were more expensive in Peru than in the supermarkets in my home town. But hey, if you pay 100 USD per day for a guide, who cares that a small jar of peanut butter costs 4 USD.
As for the Ishinca valley, Ishinca and Urus Este are among the easiest climbs in the Cordillera Blanca, and I reckon Tocllaraju still qualifies as fairly standard. However, since I had a partner, we climbed Tocllaraju unguided. Ranrapalca is a more difficult, more dangerous and longer climb, so I fully expect it to be more expensive. On the other hand, if you have a guide for 8 days or so in the Ishinca area, well, only the day that you climb Ranrapalca will be a very big one so you can try to negotiate to pay the regular daily rate for the whole period, including for that big day.
Now that you've got me thinking about the Ishinca valley, I should mention that Ranrapalca is one of the mountains I'll consider climbing myself if I return to the Cordillera Blanca. I have no concrete plans just yet, so it won't happen in 2016, but who knows what the future brings. I know that Ranrapalca isn't a mountain for which it's easy to find a suitable partner. And it's definitely not a mountain I think I can climb solo; much too dangerous for that. So, if I decide to go for it, I will probably end up hiring a guide myself. But only a guide, no porter or cook. Mules can carry our stuff to the Ishinca refuge, and from there we can carry everything to high camp ourselves. And I'll do the cooking.
Early morning on the Ranrapalca N face, seen from the approach to the SW ridge of IshincaBy the way, this face wouldn't be the route I would consider climbing, but it sure looks pretty!