Hi Jay,
1) Is the free trial account the best way to build on the SAP HANA platform without incurring huge cost? Are there other options?
It depends. Besides the free HCP trial account, there is SAP HANA Developer Edition. With the free HCP trial account, you don't need to pay anything, but you do not have OS-level access and you share the SAP HANA system with others. Compared with the free HCP trial account, when you use SAP HANA Developer Edition, you need to pay the cost of instance hourly/monthly to the cloud provider, e.g., AWS, but you own the instance and thus have the OS-level access.
2) How do I transfer files to the trial account so that I can execute a ctl file import?
As I answered in 1), you don't have the OS-level access. Although there is document services in HCP, I don't think it can be used in your importing case. So, you cannnot transfer files to the trial account for importing. However there's a workaround. You can import from your client (desktop/laptop), but it'll take more time for importing. I've tested it and it worked for my trial account.
Best regards,
Wenjun