Most designer are underpay because there's way too many people applying for the same job.
To get a high salary, you gotta be smart. Look for the ones that have less people applying.

For example : Event Designer (concept / 3d) , Product Designer .... etc

Or, other way is, have a great and polished portfolios. Simple as that.
If you have a good portfolio + a decent amount of work experience ,
even the one posted on jobstreet with a low salary will call you for interview no matter what you put
for your expected salary.

And getting a freelance job also isn't that hard. The hard part is, getting your client to pay, and pay on time.