As I understand the bank guarantees, they are only for clients of the bank, and you have to have a history with them before they will secure your guarantee. My wife looked into this for her brothers and that was the answer she got.
The link to Montclair spells out some things needed, including income statements from all included in the contract on the renter's side. I'd bet that for a foreigner, with income outside the country, it would not be very likely to happen. If you have income here, the calculator looks like it's looking for about 35% as the limit to how much of your net monthly salary needed to qualify for a guarantee. $3500 pesos a month for rent (including expenses) requires $10,000 a month in net income.
I have a friend who has consistently rented apartments with two year contracts and has never had a guarantee. Once he had to put up six months, but the other times they accepted the normal deposits. His current apartment is across from Recoleta Mall, not exactly a shabby area, so decent places can be had in this manner. In fact, this is one of the few modern apartments I've been in in BA that even has central air and heating (local to the unit) and a dishwasher, all in one.
As French mentioned, it's all about talking. My friend would spend months walking through various neighborhoods, talking to porteros of buildings he liked, and would ask the porteros if there was anyone looking for a tenant. He'd have a conversation with the owners and see if they were amenable. It takes time to find someone, but they're out there.
I knew another guy who returned to New York about two years ago who managed to rent half of a run-down PH in Parque Patricios without a guarantee. I don't remember how he made that acquaintance.
I have never had such luck - every time I've needed to move I was in a hurry and didn't have months to look. My first long-ish term rental was actually taken over from an expat I met through my friend mentioned above, who had to return to the States for business reasons. He had paid his entire contract up front and offered me the remainder of the contract as a sublet, about 13 months.
After that, I got a guarantee from an Argentine friend of mine for a house out in Pilar. His property was actually in Cordoba, and it's extremely unusual if someone is requiring a guarantee to accept property that is not local. I think I probably could have convinced them to rent to me without a guarantee because of that, but I didn't know enough then to try to get around it.
In the apartment I'm in now, I have a Dutch friend who owns an apartment here in BA who let me use his apartment as a guarantee. My contract ended at the end of April this year, and the owner and I came to an agreement (officially signed contract and all) to rent the apartment continuing on with the terms of the original contract on a month-to-month basis.
It is indeed all about making contacts and finding the way to accomplish what you need. It is a frustrating thing about BA, much like getting anything else done - the amount of time needed to secure long-term living space is just ridiculous in relation to how long something like that ought to take, for foreigners without property and history here. But there you are, one of the things about staying here long term that you have to overcome.
As far as cost - $15,000 pesos may be possible these days, depending on what you want. You might be able to buy cheap and/or used stuff and get close to that. I was lucky, I furnished mine for $4K USD five years ago when it was 3-1. But also, I just bought all the furniture that the expat who gave me that first long-ish term rent already had.
I'd say you may be looking at maybe $25000 pesos now, depending on what you want, but including a bed (personally, I have to have a king [and a room big enough to hold it!], even if I'm sleeping alone...), a refrigerator, a washing machine (not have-to-have), a microwave, a kitchen table and chairs, a sofa and a couple of chairs, a TV, knives, silverware, plates, glasses, cooking utensils, blender, etc. If you need to furnish a place to work add some more, etc.
