Extracting a specific substring in C

I have a string like this:

char buffer[] = "blablabla$GPTXT->SOME CODES HERE<-\r\n$GPRMCblablabla";

It is sent from an external device and changes every 1 second.

The string length is over 1000 bytes and consisted of some standard sentences beginning with "$GPXXX" and ending with CRLF. I've written the following function to extract a specific sentence:

int findString(char *src, char *dst, int desLen, char *what2find, char termChar){    char *temp;    temp = strstr(src, what2find); ;    if (temp == NULL)        return 0;    else        temp += strlen(what2find);    int j = 0;    while (j<(desLen-1))    {        if (temp[j]==termChar)            break;        dst[j]= temp[j];        j++;    }    dst[j] = '\0';    return 1;}

So:

 int main() {  char buffer[] =       "$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47\r\n  $GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39\r\n  $GPGSV,2,1,08,01,40,083,46,02,17,308,41,12,07,344,39,14,22,228,45*75\r\n  $GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A\r\n  $GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48\r\n";  char dst[50];  findString(buffer,dst,50,"$GPTXT",'$'); }

finds and return the desired sentence.

But this code has the following problems:

1. It is very heuristic. I wonder if there exists some better solutions.
2. It depends on a character (i.e. '$') for termination. It may terminate after finding a '$' but not "$GPXXX". The optimal solution may find the characters between two strings, e.g. "$GPTXT" and "$GPRMC". I don't know if it is optimally achievable.

Note that the host processor is a 4Mhz ARM MCU!

P.S: The above-mentioned function works fine in my project. I just want to widen my C programming knowledge!

P.S. 2: Both answers from Lundin and David C. Rankin are nice. Unfortunately I can not accept both of them as answer!