I have run nitro since 1978 (due the math) so I have a bit of knowledge on costs. I have built and set up nitro record boats and FE record boats. It took years to break into a 24 second 2 lap with an OB tunnel. Motor. carb, pipe not cheap and maybe 100+ glow plugs testing, pistons bearings and gallons of nitro. All wore out and gone.
My first FE record tunnel (same model Vision) still holds Q-S-T records 24 and 23 second records with a motor and esc about $500. My current Q mono will run under 13 second per lap for 6 laps. with a $300 Castle and a $150 TP. $200 worth of batteries which I still can run. Today 2 burnt plugs and a gallon of fuel $80. Can't reuse them.
My P/l hydro has run under a 22 second 2 lap at trials $60 motor and $50 esc. On the big end my RR E-Max with and the new Castle XL2 and a TP 4070 ($600 of power you can buy over the counter) broke into the 16's for a 2 lap. All still running. Show me nitro mono, hydro and tunnels that will come near these costs. You CANNOT! Yes, I have burnt up plenty over the years but the new out of the box Castles have addressed the weakest point of FE- ESC's
Your choice to run nitro but at $10 a glow plug and $60 a gallon fuel I won't be building any new nitro. OS 21 OB are over $700.
Mic