If you decide you don't want a jungle lodge, the Aguada Hotel near San Ignacio is excellent; for US$25-30 double you get a nice clean newish room, A/C and there's a pool.
For a moderately priced jungle lodge, I'd say you should look at Banana Bank near Belmopan, the safari camp at Chaa Creek (US$100 for two including meals), Crystal Paradise on the Cristo Rey road and the less expensive digs at duPlooy's. Two places that aren't really jungle lodges but are sort in the bush are Nabitunich and Green Heaven. Clarissa Falls also is in that category.
If you'll go to our Belize First Web edition at www.belizefirst.com
and then click on the Belize First Mainland Guide, you can download free a couple of my chapters on Cayo which lists and rates these all all other hotels in the district plus provides other current info.