The word "grid" usually refers to a two-dimensional structure while in your situation, if I understand correctly, the money given depends only on the distance to A. I am wondering if it would be more convenient to model this using a one-dimensional line.

Obviously, there are many solutions. You could give $1 to 150m, $2 to 50m, $3 to 30m, $4 to 10m and the rest to 2m. Or you could give $1 to 150m, $3 to 50m, $4 to 30m, $5 to 10m and the rest to 2m. Or $2 to 150m, $3 to 50m, $4 to 30m, $5 to 10m and the rest to 2m, etc.

You need to select the law that says how money decreases with distance. This could be a linear law, quadratic law, exponential law and so on.

Consider the linear law: the money y(x) given at distance x is -a/x(max) * x + a for some constant a. Then y(0) = a and y(x(max)) = 0. We want y(2) + y(10) + y(30) + y(50) + y(150) = M. Let S = 2 + 10 + 30 + 50 + 150 and let n = 5 be the number of grids we consider. Then y(2) + ... + y(150) = -a/x(max) * S + n * a = M, from where a = M / (n - S / x(max)). Knowing a, we can find y at each point.