I'd say come, but don't expect to be hanging out much in barrios like Palermo on that budget. It'll be more like Parque Patricios for renting and old school restaurants / parillas. That said you can get decent Peruvian food in Abasto (not at the shopping mall though, eating at the mall is more expensive than going out to a lot of restaurants -- and forget McDonalds, it's 2-3x the price of the States).
A gaseosa (coke) in any restaurant these days is 9-10 pesos. At the kiosco it's 5pesos. A bottle of water at a restaurant is about 9-12 pesos. Empanadas for delivery in Belgrano area at least are averaging around 5 pesos these days (when I got here in 2005 they were .80 centavos).
So come on down, but do not, do not believe the mythology of the $10 steak and wine dinner. As I said on another thread the other day, those bloody articles on the internet about how cheap it is to dine out in Buenos Aires are never going to die, and most of them were written 2003-2006.
You say you're not going to need to replace towels / sheets -- well then you better bring them from home because the ones they sell here are either 1) cheap and last maybe 10 washes and are horrible or 2) 2-3x more expensive than in the USA.
To give you an idea, we went to the supermarket the other week -- apart from some bread (1 loaf = 10 pesos), milk (1 liter = 5pesos), butter (500 gr is now about 15pesos) the only stuff we bought were cleaning supplies and paper products -- toilet paper, serviettes, paper towels, bleach, bathroom cleaners, detergent, PineSol, Mr Clean that sort of stuff. We brought home 5 bags of groceries and spent over 400 pesos. 30 pesos of that were edible products. We had to buy a new pot (120 pesos) and a new pizza pan (45 pesos).
So come, but don't be shocked when your money doesn't go too far. Every time my husband goes on biz to the States I basically force him to go to Target and stock up on toothpaste etc. Toothpaste in the states -- huge tubes (probably 300 gr?) for 12 pesos (Colgate or standard brand) Toothpaste here 90gr for about 12 pesos. Razors are bloody expensive, shave gels, deodorant etc -- all of those things you use everyday (unless you grow a beard) and the sizes are all smaller than in the USA.
I know you say oh I'll fit this into my 250 pesos, but you have to remember that everything here is in smaller sizes than in the USA and you have to replace things a lot more often. Have a look at your budget for toiletries in the USA and basically double it, because if the price isn't higher here, the size is smaller, so doubling it will usually work out ok (and if you're lucky, will give you a higher number, leaving you with some more breathing room when you arrive!)