How to get more neutral bar slots in my panel

[Mitch Felton]

I have a Siemens G3030B1150 panel in my house and am working on finishing off my basement. I need to add 4 circuits to the panel. I have enough room to add the breakers, but I don't have enough room on the neutral or ground bars for the additional circuits. I have a service disconnect outside of my house at the meter. Inside the panel there is one neutral bar and one ground bar. Both bars are separate (i.e. no bonding strap between them) and the ground bar has the bonding screw installed. Talking to my city inspector, it sounds like I can double up on the ground wires on the ground bar so that would take care of that side of the problem. However, I'm not sure how to best get more neutral spots. I attached photos of the panel, ground bar, and neutral bar. From what I've been able to figure out I have the following options.

Try to move the neutral lug up 2 holes to the top of the neutral bar to uncover 2 more hidden slots.
Buy some sort of neutral bar kit that would allow me to add another neutral bar. Then I would have to somehow bond the 2 bars together (maybe with 2 lugs and some large gauge wire?).
Replace the existing neutral bar with a longer bar (it looks like there's room for a longer one).
Add new ground bars to the panel case at the bottem and move all ground wires to there, remove the bonding screw, and install a bonding strap between the existing neutral bar and ground bar to make them both neutrals

Any suggestions of other options I could do? Which option would be the most preferred? Also I'm having a terrible time finding Siemen's parts to even see if some these are viable options - any suggestions on where to get them? Thanks in advance!

[John Ghent]

Purchase an additional box with as many circuits as you think you might need and feed that from a breaker on the existing panel. But, your four suggestions would also work. The downside is that if you have to ask the question then you maybe should get an electrician to do it for you as you obviously don't have the confidence to make the decision. Bad things happen when you don't know what you are doing.

[Nick Ostrowski]

Try this.

[Benjamin Thompson]

Wire nut them together with a larger conductor to the bus.

[Mitch Felton]

The subpanel is definitely a good option. Thanks for the suggestion.

Regarding the wire nutting them together, would that be up to code?

[Mitch Felton]

I have a doorbell transformer that has the hot doubled up onto my living room breaker, but both are terminated on the neutral bar separately. I spoke with one of the inspectors and they said that it is ok for me to wire nut those 2 neutrals together and then pig tail it to the neutral bar. That along with sneaking the main neutral wire back a little bit to uncover another terminal gets me the 2 additional neutral terminals I needed. Much more simple and cheaper. Thanks everyone for the suggestions.