The minimum deposit needed to open a secured credit card account is $200.  However, with a secured card, your security deposit represents the amount of credit that will be extended to you, so the higher the deposit the higher the credit line.  The activity on a secured card is reported to the major credit bureaus the same way the activity on an unsecured credit card is reported.  Given that lenders like to see that you have been extended long lines of credit, a large deposit on a secured account looks favorable on your credit report.  Plus, if you plan to make purchases with the card, a larger deposit will get you more usage.

If all you have right now is $200, then go ahead and apply for your secured card now.  You can add more money to your deposit account, thereby increasing your credit line, any time you like.