You can use:
<?php
$totalQuote = ($row_rsQuotes['total_flats'] * 75) + ($row_rsQuotes['num_of_blocks'] * 500);
if ($totalQuote<1000) $totalQuote = 1000;
?>
<input type="hidden" class="form-control" name="quote" id="quote" value="<?php echo($totalQuote); ?>">