Since there are only four main lodges in the Mountain Pine Ridge reserve itself -- Blancaneaux, Hidden Valley, Four Sisters and Pine Ridge Lodge -- and all, especially the first three, are quite expensive, you might look at lodges just outside the Pine Ridge, such as Moonracer Farm, Inn the Bush, Crystal Paradise and Barton Creek Outpost, or even budget/moderate places in San Ignacio/Santa Elena such as Aguada, Marthas and Casa Blanca Guesthouse.
Discounts of around 50% on lodging (though usually not meals) are often available to Belize citizens but usually off season rather than in high season, which is now.