TL;DR 34000 minimum but just to be sure, get at least 35000, in case there are large fluctuations on the last 2 days.
I took note of fame points required for 8000th place after every day of a campaign. It starts from 2. day. Numbers are rounded to closest 5 or 10 so there is +-4 difference at some points.
Math behind it is this:
| Day of campaign | Total fame points for 8000th place | Difference to previous day | Difference between increases |
|---|---|---|---|
| 2. | 650 | 0 | 0 |
| 3. | 1665 | 1015 | 1015 |
| 4. | 2620 | 955 | -60 |
| 5. | 4340 | 1720 | 765 |
| 6. | 6240 | 1900 | 180 |
| 7. | 8565 | 2325 | 425 |
| 8. | 11220 | 2655 | 330 |
| 9. | 14285 | 3065 | 410 |
| 10. | 17615 | 3330 | 265 |
Campaign lasts for 14 days, so 4 more days to go.
As you can see, the number of fame points for 8000. place increases exponentially each day. Although on the 10th day the increase seemed to slow down a bit, it might be attributed to some clans "leaving" the map (trading captured provinces and clan fame points for research points) so less players are playing x5 battles.
My projection is that it is going to increase by 300-350 every day, or maybe even more in the last day or two of the campaign. So by the end of the campaign, it will require minimum 34k points for a tank, but just to be sure, I suggest getting 35k.
Also worth noting is that you should have gotten 2500 boost to personal fame points by now if you think about going for a tank, since it pays off after you earn next 20k points. Boost that costs 5000 points was worth getting if you are planning to get 35k+ points after purchasing it so its not recommended (if you are going just for the tank and not top places in fame points).
P.S. Last campaign that had 8000 places for a tank, required 20600 fame points for a tank, but it only lasted for 10 days.
