The Atterax is a good crit-slash weapon, one of the best not prime melee weapon, accessible at the mastery 5, and don't require specific resources. (only 2 argons, that can be found anywhere in the void with some try)
An other very good weapon for the beginning is the [Guandao], accessible at MR4, but need a dojo (so join a clan). with the same build as this.

With this build, you can kill ennemis at level 100.

Before use an Orokin reactor, use the first line of mod.

Virulent scourge can be fund on Vor in the last part of the void. (it has 0 cost, someone can give it to you ; or you can use a not-maxed [Fever Strike])

Berserker is the only mod a bit hard to find.
You can trade it to an other player, the cost are low. (or ask to someone of your clan)

(The high cost version of this build is : https://overframe.gg/build/20846/ .
But your build will not look like this before a huge amount of hours played :
First, the endo cost is 200 000, when for the low cost, it is 3500.)