While there are several inverters with 450-500V mppt input sometimes in higher power units even two of them, I cannot find and standalone mppt charge controllers with 450-500V input .. is there any out there at a reasonable price?

Ah. Maybe that's because bucking 500 down to 50 V is very inefficient and/or difficult to control (small changes in the PWM ratio makes a large change in the battery current). But in an off-grid inverter, which already has a transformer based 500 V <-> 50 V converter, boosting from say 200 V (panel voltage) to 340 V or so (bus voltage) is fairly efficient (not such a wide voltage range).

But maybe a transformer based solar charge controller would not be too expensive, I have no idea.

2 hours ago, burgduino said:

While there are several inverters with 450-500V mppt input sometimes in higher power units even two of them, I cannot find and standalone mppt charge controllers with 450-500V input .. is there any out there at a reasonable price?

Victron RS 450/100 available in a 5.76kW and 11.52kW model, Mppt range 80-450 VDC operating solar voltage input, but they are expensive.

https://www.livestainable.co.za/product/victron-energy-smartsolar-mppt-rs-450-100-tr-solar-charge-controller/?gad_source=1&gclid=CjwKCAjwxNW2BhAkEiwA24Cm9L_gbaijdh3UmwUDCFVSWsmLffBg_iBIcp3JIrDtebtunBTV4pBpnBoCNVQQAvD_BwE

21 minutes ago, TaliaB said:

Victron RS 450/100 available in a 5.76kW and 11.52kW model, Mppt range 80-450 VDC operating solar voltage input, but they are expensive.

https://www.livestainable.co.za/product/victron-energy-smartsolar-mppt-rs-450-100-tr-solar-charge-controller/?gad_source=1&gclid=CjwKCAjwxNW2BhAkEiwA24Cm9L_gbaijdh3UmwUDCFVSWsmLffBg_iBIcp3JIrDtebtunBTV4pBpnBoCNVQQAvD_BwE

Even if I win the lotto I could never pay this for a MPPT only. Yes I know they are very good products. 

My call would be to just use more strings and buy 2 x 240V MPPTs.