DAZ211 - have you done your research about what is on offer at Southend at all? There are between 2 trains an hour (off-peak) and 7 an hour (peak) between Southend airport station and Liverpool Street. Not greatly different than at Stansted on average I suspect, but bound to be cheaper.
I think I heard that it was 50 something strides from Southend station to the terminal, and it will be a covered walkway too. Station staff are employed by Stobart also, which means that it is all done by the same team. I know which of the two I would choose to travel from given the choice, small and friendly or not so small and friendly.