$30 a night doesn't sound to bad, it is below the mean of what I've been paying for overnight sites in full-hookup RV parks for the past 11 years. My experience has been mostly in parts of the country (Missouri, Illinois, Indiana, Michigan, Iowa) where land values are much lower than typical along the Eastern Seaboard, but not as low as in rural Texas, Oklahoma, and New Mexico where an overnight might be more like $22-26.
A lot higher anywhere for proximity to a city or vacation destination, just as the same motel room might be $80 or $400 depending on location, or a similar size apartment rent for $800 to $4000.
$900 a month sounds pretty good for an apartment in Maryland if it is close to a city.
RV parks on a monthly basis are often about half the price of 30 x daily rate, but then you pay utilities as an extra.