Definition of "too expensive" is very subjective of course....
You could try Island Moorings at Port Aransas / Mustang Island. Your draft
should be fine in their sometimes skinny channel. We had our previous boat there and enjoyed the facilities / people. OTOH I was trapped in there for about 8 months with a 6ft draft
boat while they dredged the channel.
Also check out the City Marina at Palacious. It sounded great to us until we discovered 6ft draft would not get in.