▁machines ▁on ▁the ▁market ▁cost ▁$ 3 , 0 0 0 ▁but ▁the ▁brothers ▁( with ▁help ▁from ▁friend ▁Jon ▁Williams ) ▁sold ▁their s ▁for ▁$ 6 0 0 . ▁The ▁product ▁was ▁an ▁instant ▁success ▁and ▁has ▁been ▁re vised ▁over ▁the ▁years ▁with ▁the ▁Model ▁B ▁( 1 9 8 6 ), ▁Model ▁C ▁( 1 9 9 3 ), ▁Model ▁D ▁( 2 0 0 3 ), ▁Model ▁E ▁( 2 0 0 6 ) ▁and ▁Dynamic ▁( 2 0 1 0 ). ▁ ▁Until ▁ 2 0 0 6 ▁the ▁company ▁produced ▁and ▁sold ▁only ▁one ▁model ▁of ▁ind oor ▁ro wer ▁at ▁any ▁time . ▁That ▁changed ▁in ▁September ▁ 2 0 0 6 , ▁when ▁Con cept 2 ▁upgrad ed ▁their ▁Model ▁D ▁and ▁began ▁s elling ▁a ▁new ▁pro sum er - orient ed ▁Model ▁E ▁( pr iced ▁around ▁$ 4 0 0 / £ 3 0 0 ▁above ▁Model ▁D ) ▁that ▁provides ▁a ▁higher ▁row ing ▁position ▁with ▁extra ▁layers ▁of ▁paint / var n ish , ▁sh ipped ▁with ▁a ▁more ▁advanced ▁(" PM 4 ") ▁monitor ▁and ▁bund led ▁an ▁AN T + HR - compatible ▁Gar min ▁heart ▁rate ▁bel t . ▁Both ▁D ▁& ▁E ▁models ▁are ▁used ▁for ▁ind oor ▁row ing ▁events ▁such ▁as ▁B IR C ▁and ▁CR ASH - B . ▁ ▁In ▁ 2 0 1 8 , ▁Cross F it ▁officially ▁made ▁Con cept 2 ' s ▁D ▁& ▁E ▁models ▁as