Have them have a look at www.expedia.com for their travel dates to see the best rates on many of the hotels in the city.
For their price range then: IQ CAllao,Concord Callao,Etoile,BelAir,Ayres de Recoleta/Libertad/Recoleta Plaza,Urban Suites,Intersur Recoleta. These are all located in Recoleta...