If you are a big Elvis fan there is a helpful web page from Vegas.com will help you find your Elvis in Vegas. Click here for Vegas.com's guide to Elvis stuff in Las Vegas.
You may want to check out Legends In Concert at the Imperial Palace, with a big show featuring Elvis and other legends. Add the meal option which is only about $60 vs over $50 without the meal. If you are on tight budget (or just frugal), check out the discount show ticket places along the strip which often offer half price show tickets. Ask at your hotel desk for the location and best strategies to get discounted tickets.
Generally in Las Vegas if you are flexible about days, seating, and shows you can find much cheaper entertainment than if you insist on a specific headliner at a specific time, which will generally run you full price and range from $50 to $250 depending on the show.