I came up with the similar solution, just code is a bit more compact

static int getMoneySpent(int[] keyboards, int[] drives, int b) {
    Arrays.sort(keyboards);
    Arrays.sort(drives);
    int max = - 1, k = 0;
    for (int d = drives.length - 1; d >= 0; d--) {
        for (; k < keyboards.length; k++) {
            int sum = keyboards[k] + drives[d];
            if (sum > b)
                break;
            max = Math.max(max, sum);
        }
    }
    return max;
}