Sorry I really dont't understand what you mean.
model Regexp($model) - regexp() is not a php standard function
<?php
print "search.php?page=2&brand=".Regexp($brand)."&year=".Regexp($year)."&color=".Regexp($color)."&price=".Regexp($price)."&model=".Regexp($model);
?>
<?php
// normally you have to user rawurlencode(), if you want to build an url
print "search.php?page=2&brand=".rawurlencode($brand)."&year=".rawurlencode($year)."&color=".rawurlencode($color)."&price=".rawurlencode($price)."&model=".rawurlencode($model);
?>