lsfit:{(enlist y) lsq x xexp/: til 1+z};
interp:{[xn;x;y]sum (1;xn)*flip lsfit[x;y;1]};

table:([] amount:500 730 1250;xRng:(0 1;0 1;1 2);yRng:(5 7f; 5 7f; 7 10f));table

amount  xRng    yRng
500     0 1     5 7f
730     0 1     5 7f
1250    1 2     7 10f

amount  xRng    yRng    result
500     0 1     5 7f    6
730     0 1     5 7f    6.46
1250    1 2     7 10f   7.75

interp[first table[`amount]%1000;first table[`xRng];first table[`yRng]]