Funny - I just did that last weekend. They had side Mezzanine seats (way in the back on the side) for $25 each. They add a $5/ticket service fee on top of that, but you can usually find coupons for at least a buck off (they sometimes have coupons on their website). There were also better categories of seats for more (40-something and 50-something IIRC) .
Note that when you use Tix4tonight, you don't get tickets. You get vouchers for tickets, and then have to go to Mandalay Bay to get real tickets and seat selection.
Great show by the way. Enjoy.