Synchronization Problem

Dear all,

Please help me on solving the synchronization problem between two development sites.

Backgrounds:
1) A site conducts system design and development
2) B site conducts development only
3) No common repository for design documents and source files.
4) Design documents and source files sent via emails.
5) Low-Budget and policies for not setting FTP or some online tool for sharing files.

Issues:
1) Latency for document exchanges
2) Some files are missed to be sent
3) Versions of documents/files were a mess
4) File Merging requires lots of human efforts
5) File Merging generates mistakes

Any comments or suggestions to improve the situations? Please help.