[Suicide Junkie]

How about:
Remove counter intel projects.
Price of intel sabotage should be medium-low. (reduction in price as counter-intel tech rises, say)
Espionage projects should have low to medium cost depending on value.
Sabotage projects should have high to extreme costs depending on value.

low = about 10k
medium = about 40k
high = 100k
Extreme = 500k

So, the chance of success goes down with the time taken to complete the project.
The big sabotage projects would take quite a while to do, and would be vulnerable to intel-sabotage projects. Running some throw-away "decoy" projects would use more intel points, but would help your chances overall.

Someone capable of completing 12 intel-sabotage projects in one turn could completely block any multi-turn projects by one other player...
This would still allow a few cheaper projects through, but would be good protection against major sabotage.
It would also leave a vulnerability to other attackers. If the projects are split, you'd still catch a good deal of the major sabotage, though there would be a chance of success if you get unlucky on the intel sabotaging.

Feel free to tweak the numbers, these are just rough.