$dbQuery = "select * FROM highalch ORDER BY id ASC LIMIT $start,100";
$result = mysql_query($dbQuery) or die("Couldn't get file list");
$numrows = $row['numrows'];
Something missing from here perhaps?
$rowcount_query = "Select count(*) from highalch";
$rowcount_result = mysql_query($rowcount_query);
$numrows = mysql_result($rowcount_result, 0);
is what I'm guessing you intended.
Do your development with error_reporting set to E_ALL and PHP will warn you about mistakes like this (specifically, it would have told you about an uninitialized array index 'numrows').