I stayed in Peru for almost 2 years on a Tourist Visa and did the "Border Hop" when I decided to go legal. I did the math and for me it was cheaper to pay the fine than fly down to the Border do the taxi into Chile and back plus stay overnight in Tacna. I paid over $700 in fines which the Head Guy said was the largest he had ever collected.
Getting a Carnesta was rather easy. I opened an account at Interbank and deposited $1,000 USD or less and got a letter from them. I can't remember exactly how much I deposited, showed that I had monthly income in excess of $1,000.00, and completed some form. Everything had to be translated into Spanish by an official translator then I submitted the paperwork and waited about 2 weeks and was informed I was approved. Went to the second floor had my pictures, finger prints, and signature taken and got my Carnesta about 30 minutes later.
Not bad considering some lawyer who frequents this board who claims to be the only "honest" lawyer in Peru wanted to charge me $500.00. I think I paid s/. 90 for the translations. The thing that can bother a lot of us is the time you have to wait from when you submit your paperwork to know if you are approved because you have to return to their offices to find out. I just simply doubled the time.