I have 8 of the Driftmaster T-275-HC Crappie Stalker Gunslinger style rod holders.
Designed to totally isolate rods and eliminate rod movement. The T-275 puts each rod with its own T-bar; eliminating movement of one rod while adjusting another. T-bar components allow unlimited adjustment in any direction. Low profile
allows holder to be folded down close to boat when not in use. List $72.00 ea.
The Crappie Stalkers have the 3/8 inch thread, and are tall.
Driftmaster does not sell the correct base for these separately, but if they did, I would estimate that they would cost about $30 each.
Thus, I think the Rod Holders with bases are worth at least $45 each ($270). I have 6 complete & two (2) extra bases for a total of $330.
The entire set of 8 cost me $576 plus $30 shipping. ($606 total).