I wrote a couple functions to do what I suggested, although I didn't test it very extensively, so use at your own risk:

#include <stdio.h>

#define NUM_CHARS 8

void    floating_dollar(float f);
int     num_chars_float(float f);

int
main()
{
        int i;
        float f[5] = { 1.1, 0.5, 13.8, 102.19, 4172.91 };

        for (i = 0; i < 5; i++)
                floating_dollar(f[i]);

        return 0;
}


void
floating_dollar(float f)
{
        int count;
        int i;

        count = num_chars_float(f);
        for (i = 0; i < NUM_CHARS - count; i++)
                        putchar(' ');
        printf("$%.2f\n",f);

}

int
num_chars_float(float f)
{
        int num_chars;

        num_chars = 0;

        if (f < 1)
                return 1;

        while(1) {
                if ((int) f == 0)
                        return num_chars;
                num_chars++;
                f /= 10;
        }
}