Modern tank, truely proportional control, 16th scale and 'decent' well the Tamiya Leopard 2A6 is the only contender satisfying all these and it can be purchased for about 800 dollars on Ebay.

The next satisfing your criteria may be the Hen long Walker Bulldog or the M1A1 by RipMax.

The 24th scale moderns (VStanks) are quite good in quality and function for their size and price.