If you are updating this once and day, and it's your database, important, but not affecting others, here's what I'd do.
Change the database to simple mode. With updates once a day, no real reason to recover to a point in time (outside of the backup). If that's no the case, don't do this, but if you only care about recovering in a disaster to the time of the backup, this works. However before you do this, I'd run a log backup before my load/change, then load/change and run another log backup. This second one gives you an idea of how big your log should be.
Run a full backup before each load. You could do it after, but if the load fails or there's an issue, I'd prefer to have a recent backup and not assume that yesterday's backup is there. Copy this off the disk to another location immediately.
Now you should be able to shrink the log file to roughly what you found in step 1 above, with some pad. I'd only shrink the log here, not the data file. Use DBCC SHRINKFILE.
Ultimately you need space for the data, so you'll need that much disk space. I'd also recommend you read Gail's article so you understand what you're changing here.
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