Roomba lifetime costs

Roomba 550 cost about 2-300 US$ about 10 years ago at Cosco. Is in third battery now, after a battery lifetime down to about 5 seconds. It is cranking now. Very good. We have doghair now and this accumulates! Blocked the black/white front passive wheel IR sensors! For about 10$ a year for battery ($30 every 3 years) and maybe $5/yr for filters, replacement brushes etc, its pretty good. Amortized over 10 years: 300 + 10 * 15 = 300 + 150 = 450 / 10 yrs = 45 $/yr to clean the floor autonomously, when we're not home. Nice. ROOMBA and MIT and HAL, SCORE! Also, being in consumer electronics now, I see some of the problems they would have or did face, eg chinese plastic that deforms under stress... But they replaced these easily and Ms. R. continues to work! (I also used some low-temp-softening nylon prototyping plastics to fix a pair of self-fastening screws on the bottom of the 'bot. This saved me about $30 for the stupid replacement part. And saved "duh erth" from "du landfill" <---- fur dur erf moronz And for the price of a pair of "C" batteries one of my walls is working so I can leave Ms. R. to tend to the intended area. peas and doves