Hosted file sharing/storage solution recommendation needed

I have a small branch office in Singapore that is in need of a file server.  Problem is the office is too small to invest in the infrastructure and security equipment necessary to install a physical infrastructure.  That and the fact that they are renting shared office space with a network shared with another company (they are basically using the other companies network for internet access only).  They currently are refusing to save and access documents from our EU data center, due to the latency VPN causes from Singapore.  

I have given thoughts to setting up an AWS infrastructure (Amazon has an AWS infrastructure in SG) and allowing them to VPN to a Windows file server within, but AWS isn't quite secure enough for my taste just yet.  Plenty of monitoring and IDS options, but no active IPS yet that offers the security our clients would require.  There are a couple solutions on the horizon that remedy this, but not for a while.

So for now, I need some form of a highly secure file sharing solution that the users can access from their PC's (again, no infrastructure there).  If one exists.  Thanks.