You don't need many tools to assemble an ar lower.
I did my first few with a hammer, channel locks, and a cheap castle nut wrench.
And they came out fine. No scratches at all.
The proper tools to assemble a lower will probably set you back less than $50.
Its worth it because these won't be your last that you assemble.
Check you the build it yourself sub forum in the AR15 forum.
Step by step instructions. That's how I assembled my first few