The Sheraton at Sand Key has a great beach, and might be more in your price range than the Don Cesar, although I've only stayed at the Sheraton. It's an older property, but the pool is great, and you just walk right on to the beach. Some newer properties in that area have far less desirable beaches. Rooms at the Sheraton are just your basic hotel room with balcony, but I thought the beach-pool area made up for it when I stayed there.
The Don CeSar on St Pete beach is quite wonderful but unless you go off season or can catch a special it will probably be above the 150 price range. It is a "grand" old hotel with lovely public areas and a very nice beach. I've heard pretty good things about the Tradewinds Resort and The Bilmar Beach Resort(I haven't stayed there in years so can't be sure). The "Don" is worth a splurge if you really want a nice place.
