I got papers from Mauritius Immigration (First Schedule Reg 3) & list of documents when I was there last year. They required and I quote
"Documentary evidence of latest financial means for the upkeep of oneself and that of his family (which should include bank statement, payslip, pension slip, etc)"
Based on this and what I have read I understand the income is not needed to be a lump sum but a regular source for retired people with overseas income coming in. You might also qualify if you set up a business in Mauritius and have income earning of a particular minimum from my readings but I can't tell you the precise details. You'll likely find them on the following site somewhere :
I am unsure of anyone specialising in this area in Mauritius but the man at Immigration was very helpful to me. Your nearest Mauritian Embassy or Consulate might also be able to help.
I have just returned from Mauritius and you should find reasonable accommodation for 25,000MR per month. The quality will depend on where you stay. I saw some good accommodation in Beau Bassin (fully furnished near Balfour Gardens) for 18,500MR/mth - this is a "town" just south and up from Port Louis not far from Ebene (Cyber City). I also saw some in the north around Trou aux Biches ranging from 15,000MR to 25,000MR and these varied greatly in quality of accommodation and furnishing.
There are estate agents also that deal in rentals & they normally charge 1 months rental for their service.
When are you planning on going ? Depending on when you intend to go and where you choose to stay I may be able to put you in touch with someone on the accommodation side.