The cheapest Si unit we have is the 798ci Si, but you were not wanting the cheapest so you I will list them in order of cheapest to most expensive:
898c Si
998c Si
1198c Si

Basically the differences between these units is the size of the display. Extra unit mounts, power cables, transducers, GPS Receivers and connector collectors are available for them but will cost some $$$.
Power Cable: PC-11
Transducer: XHS-9-HDSi-180-T
GPS Receiver: AS-GR50
Unit Mount: GM-2 for the 898/998 and GM-3 for the 1198
Connector Collector: 540165-2 for the 898/998 and 540178-1 for the 1198