"Best" and "entry-level" shouldn't be used in the same sentence.
The "best" Nikon full frame DSLR is the D850, which is a 45MP camera that sells for around $3000.
The "best" full frame Nikon telephoto zoom lens for wildlife photography is the AF-S 180-400mm f/4 1.4X FL VR. This lens has a built-in, matched teleconverter that can be engaged at the flip of a lever, to make for a 252-560mm f/5.6. This lens weighs about 8 lb. and costs around $12,000.
560mm on full frame is not really long enough for a lot of wildlife, so might also want a "best" Nikkor AF-S 800mm f/5.6 FL VR, which weighs about 10 lb. and sells for a little over $16,000.
Not very "entry-level" priced, eh? There are less expensive full frame DSLRs and full frame capable lenses, but I would say expect to spend at least $2500 to $3000.... and probably more.
For wildlife and affordability I would instead recommend a much less expensive and more practical, but still very capable APS-C "crop" sensor camera. The crop camera "leverages" telephoto lenses, making them act like they are longer. This a big advantage for sports and wildlife shooters, allowing them to use considerably smaller, lighter, less expensive lenses!
Look for a refurbished D7200, which is a 24MP APS-C camera. This model has been replaced by the D7500, but while the newer model has a faster frame rate, it is a bit lower resolution (21MP) and gave up some other features that were on the D7200. A refurb'd D7200 can be found for $694. The D7500 sells for $997 new or $699 refub'd. There are less expensive Nikon cameras... D3000-series and D-5000 series... however they have some limitations. They are unable to autofocus some Nikon lenses, for example. The most entry-level Nikon D3500 with two lenses (18-55mm and 70-300mm, where the latter doesn't have image stabilization though it would be very helpful) costs close to the same at the refurb'd D7200. A slightly more upgrade D5600 camera with only an 18-55mm lens can be had for under $500 right now.
Even so, I'd recommend the refurb'd D7200. The D7000-series cameras are more versatile, better built and have many more advanced features. They would be a better camera to "grow into" over time.
With D7200, he'd still need a telephoto lens. I'd recommend Tamron 100-400mm as a good option that sells for $799. On an APS-C camera, this lens will "act like" a 150-600mm would on full frame! But it's a lot smaller and more affordable than a 150-600mm or Nikon's 200-500mm. Sigma also makes a 100-400mm for the same price. I like the Tamron better because it can optionally be fitted with a tripod mounting ring (sold separately for around $129, but can add it later). There is no option to fit a tripod ring to the Sigma... and I would want one for such a long telephoto.
There also are 70-300mm lenses for less. Nikon's AF-P 70-300mm DX with VR sells for half the price of the above 100-400s (all of them have VR, VC or OS image stabilization, too). It's a fairly compact lens, but 300mm will come up a bit short for a lot of wildlife photography, even when using it on a crop camera (where it "acts like" 450mm would on full frame).
D7200 refurb'd doesn't appear to come with a shorter, general purpose walk-around lens... but there are a number of those to be had...Usually the least expensive zoom is 18-55mm. IN fact, B&H Photo has those refurb'd for all of $69 right now (reg. sells for $247 new).
"Best" and "entry-level" shoul... (