In Texas, any adult person can apply on behalf of an applicant who is unable to appear personally before the county clerk. An affidavit of absence form must be provided when you apply to the clerk's office where you are to be wed. The application fee for a marriage license is $60. Doing a marriage by proxy will probably add additional expenses but it can be done over the internet or a stand in can be appointed for the ceremony. It's would be valid if the clerk accepts your application and provides you with a license.
This is not legal advice nor does it create an attorney-client relationship. This is for education and informational purposes only. It is always recommended that you contact an attorney with any concerns as each individual case is unique.