To further clarify: there is only one download/installer of Capture One. When you download it and run it for the first time (or later select "License" from the menu) you can select from the following options:
- Capture One DB: Free and 100% feature complete, but only works on Digital Back files
- Capture One Pro: Same as Capture One DB, but costs money and also works on dSLR files.
- Capture One Express: A "lite" version of little interest to pros or enthusiasts
- Trial: a temporary one-time-only full functional trial, no watermarks or limitations (other than it expires after X days)
Capture One Pro 6 is coming towards the end of it's life; a new version is expected sometime this year. Upgrades have been historically pretty affordable, and if you happen to purchase very shortly* before a new version is released you can contact support or your Phase One dealer and they will get you a free upgrade. For this reason you shouldn't hesitate to buy C1 v6 now even though v7 is expected in the coming months.
Phase One has been running a lot of promos for pricing on C1 in the last three months, presumably (though not for sure) related to some combination of the slower summer months and a new version being imminent. This week it's 50% off at phaseone.com. I believe you can still use the promo code "DT3535" to get an additional discount, but honestly the sales have been so frequent and varied that it's hard even for me to keep track of (especially since I'm not in the sales department).
I suspect pricing will return to a fixed $299 with only a sale or two a year (as was the case before a few months ago) once Capture One 7 is released.
*Usually defined as 30 days, similar to other stores like the Apple Store