What is the best Micro lens for a Nikon D3400 Camera?

What is the best Micro lens for a Nikon D3400 Camera?

Added (1). One which isn't too expensive, if possible please

The one you can afford.

Depends on what you are doing and what you consider expensive.

If taking pictures of bugs or small jewlery, something near 100mm focal length. The longer focal length gives you more working room between the end of the lens and the subject.

Flowers, 60mm or longer. This is also a good portrait lens for your camera.

Artwork, 40mm or longer. This is also a good prime focal length for general shooting.

Nikon's 40mm lens is affordable. The 60mm is less affordable. The 105mm is expensive.

The best bang for your buck is Tokina's 100mm f/2.8 macro (micro, in Nikon parlance). The optical quality is very good. The bad about this lens is it won't auto focus on your body (need focus motor in the body). I don't think I've ever used auto focus on my macro since it's mainly for closeup work or product shooting.
Also, high contrast edges will have some chroma-flare and there's no VR. If doing macro work, VR isn't that important since you normally shoot from a tripod.

Sigma and Tamron also make good macro lenses.

There are methods of doing Micro photography without buying an expensive Micro lens. Two of them are reversed lenses and extension tubes. Search for those two things for more info. Meanwhile, this link will tell you some of the things you need to know.

I use a 50mm F1.8 and an M2 extender ring. Manual focus with the ring. I also have an older 55 macro that works great and came with the M2 ring.
A newer faster focusing AF would be the 40, 60 or 105 macro/micro that Nikon has but these are more expensive.
The 105 will focus close and allow you to be further away from touchy subjects like dragonflies at rest.

Since your in the UK, I use a sigma 70-300 macro telephoto lens, available from Curry's for £124.

You can use it in manual or auto and has a dedicated macro switch on it.

Micro? Or did you mean macro? A world of difference.