It would help if you could define "cheap" since cheap is relative. If you don't care about fancy and want peace and quiet, try River Lodge RV in Inglis FL on US Hwy 19. They have back in sites including water, sewer, electric, wi-fi and 70 channels of cable for $500 per month (current rates). Shady grassy sites. Read reviews on www.rvparkreviews.com under Florida> Inglis.
We like Williston Crossing RV Resort in Williston FL. They have a few grassy back in sites for $627 per month including electric (current rates). Their paved sites are $627 per month but you pay your own electric. Nice resort with all amenities. Small town location. During the winter in Florida it's difficult to find spots that are cheap.
Also try Sumter Oaks Escapees park in Bushnell, FL. https://www.escapees.com/parking/rainbow-parks/bushnell-florida/sumter-oaks-rates