Unless you just want to add to your arsenal, the rifles you have are capable of shooting at your range goal. Depending on the range and size of them aliens and zombies, with proper handloads, it you might be able to neutralize them.
For instance, with Matrix VLDs in 165/175 grain and the Berger 170 grain (soon to be available) bullets, it takes the .277 cals to a new level. If you do a search, there are plenty of threads to drool on.
There's also a nice article on .270 Win on the article section worth reading.
At $2500 rifle only budget, it gives you a lot of flexibility and you're within reach of a custom built price range.
Below is my semi-custom build for your comparison only, there are others who have done similar projects.
My budget .270 AI ...
IMHO, as far as best platform, it boils down to preference. The Remington 700 is probably the most cloned action and the Savage actions are preferred by most DIYers ... hopefully, others will chime in.
Good luck and welcome to LRH.
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