If you change the cells yourself it will cost you alot less than $500. I got my cells for $75 a piece and the fluid was something like $7 a liter, you will need about 3-4, can't remember.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member