I will agree with ZMV that permanantly attaching a suppressor to a short barrel is not a good idea, and it is not just because we build suppressors.

1. You will eventually want to put your suppressor on another weapon -- suppressed shooting is fun.
2. Cleaning the weapon will be far more difficult, and you do not want to stick a patch in the suppressor.
3. Few suppressors today use the same material as the barrel, making a tack weld impossible.
4. A blind pin still requires a tiny tack to guarantee it does not back out.
5. Tack welding (tig or acetylene) will damage the heat treatment of the end of the barrel affecting accuracy, barrel life, and probably warp alignment.
6. Few manufacturers of suppressors are wiling to try to repair their suppressor if permanently attached to another product.
7. If not abused, most suppressors will significantly outlive a barrel's accuracy.
8. .30 cal suppressors do a really good job on smaller centerfire rifle cartridges (.223, .270, etc.) as well as .308.

In my opinion, trying to save a $200 SBR excise tax is false economy when you consider the negatives. If cash flow is tight at the moment, I would suggest a good suppressor and start with a 16" barrel. As disposable income becomes available, replace the barrel. Consider a relatively lightweight suppressor of good representation, and consider a thread-on unit (which are generally shorter, lighter, and often less expensive).

Just my two cents worth.

I'm very much against pinning and welding.   I've seen customers who thought it was a good idea at the time... they ALL asked if we could remove it or recommend a smith to take it off.

You've got money into a can, money into the rifle, done the Form 4 work on getting a can.... $200 more to register a lower shouldn't be impossible.  I understand tight budgets all too well... but save up to SBR that lower.  A registered lower gives you SO many more options.  

I personally am.  

That being said, if you know the downsides and want to do it... do what makes you happy!  

I forgot to mention to the OP--- there's also options like the Leonidas that will keep you at 16"

It is your property to do with as you wish. We recommend against silver solder or tig welding. You will destroy the hear treatment on the barrel end, adversely affecting group size. The silver solder ATF approves has a melting point of 1200+ deg F.