You can use the title attribute.
For the lowest price, that would best be done when selecting from the database using the MIN() function. Group by the identifier, and it will pull the minimum price.
Can't work without any data, but that would look something like:
$sQry = 'SELECT `identifier`, `price`, MIN(`price`) AS lowest FROM myproducts GROUP BY `identifier` ORDER BY `identifier`';
if ($qry = mysql_query($sQry))
while ($row = mysql_fetch_assoc($qry))
printf('<tr><td title="%s">%s</td><td>%0.2f</td></tr>', 'Lowest Price: ' . $row['lowest'], $row['identifier'], $row['price']);
Take note though that this will only pull the lowest of the returned resultset, so if you limit it you will have skewed results. To pull from the entire table all the time, either use a second query or use a sub select query within the select. The SQL guys would be able to tell you which is better (I'd expect 2x queries to be better than 1x query with a nested select).