Well, with my cheapest option being $11.35 from Willy's Offroad Supply for a Omix-Ada replacement.
BTW, the stock replacement numbers;
Replaces Part # Years Engine Diameter Grooves Comments
CJ
J3239821 81/86 4.2L (258) 3.95" - 100mm 6 w/o AC, w/o Emission Pump
YJ
J3239821 87/90 4.2L (258) 3.95" - 100mm 6
53002905 87/95 2.5L 3.55" - 90mm smooth
53002905 91/95 4.0L 3.55" - 90mm smooth
TJ
53002903* 97/98 2.5L, 4.0L 3.95" - 100mm 6 Idler only
4792112 99/02 2.5L, 4.0L 3.55" - 90mm smooth Idler
4792112 97/02 2.5L, 4.0L 3.55" - 90mm smooth On Tensioner
53010230 01/04 2.5L 3.00" - 76mm smooth
4854092 00/06 4.0L 3.00" - 76mm smooth Includes shaft
4854089AB 00/06 4.0L smooth Complete Tensioner
SJ
J3239821 81/90 4.2L (258) 3.95" - 100mm 6
XJ
53010230 96/00 2.5L, 4.0L 3.00" - 76mm smooth Upper idler
53010230 96/01 4.0L 3.00" - 76mm smooth Upper idler - RHD only
53002903* 97/98 2.5L, 4.0L 3.95" - 100mm 6 Idler only
53002905 87/95 2.5L, 4.0L 3.55" - 90mm smooth
4792112 96/01 2.5L, 4.0L 3.55" - 90mm smooth
53010309 87/91 4.0L 4.57" - 116mm smooth At Water Pump
ZJ, ZG
53002905 93/96 4.0L 3.55" - 90mm smooth Fits 6 groove belt
53010230 97/98 4.0L 3.00" - 76mm smooth Upper idler
4792112 97/98 4.0L 3.55 - 90mm smooth Fits 6 groove belt
53009508 93/98 5.2L, 5.9L 3.55" - 90mm smooth Fits 7 groove belt
53010158 93/98 5.2L, 5.9L 3.15" - 80mm 7 Complete Tensioner
WG
4854092 99/04 4.0L 3.00" - 76mm smooth Includes shaft - metal
53030958AC 99/04 4.7L
4854089AB 00/06 4.0L smooth Complete Tensioner
KJ
53013324AA 02/05 2.4L 3.00" - 76mm smooth
5142573AA 02/07 2.5L Diesel 3.00" - 76mm smooth Includes shaft - plastic
5142573AA 03/07 2.8L Diesel 3.00" - 76mm smooth Includes shaft - plastic
5142798AA 02/07 2.5L Diesel 2.60" - 66mm smooth Tensioner
5142798AA 03/07 2.8L Diesel 2.60" - 66mm smooth Tensioner