I have been using the Sony Alpha 7 IV Mirrorless Camera for quite some time now and honestly, I couldnt be more satisfied with its performance for travel. Sony typically runs a dedicated Summer Savings event in late August or early September, so you definitely dont need to wait until Black Friday to find a deal. Comparing my experience with different glass, I personally prefer the Sony FE 20-70mm f/4 G over the older Sony FE 24-105mm f/4 G OSS. The 20mm wide end is a total game changer for Japan architecture, even if you lose some reach on the long end. The newer 20-70mm is lighter and the optics are noticeably sharper, tho the 24-105mm is still a solid workhorse if you really need the extra zoom. Everything works well together and I have no complaints about the autofocus speed on either lens. Definitely wait for that Labor Day window for the best pre-October prices.

I saw your post this morning and honestly, you really need to be careful with your budget if you want both the body and decent glass. Since you need it before October, I would suggest monitoring price trackers like CamelCamelCamel or the Keepa extension for the Sony Alpha 7 IV Full-frame Mirrorless Camera Body. I have seen prices drop randomly for 24-hour periods that arent even part of a major event. Basically, if you want to save money for the actual trip, you might want to consider these resources:

• Make sure to check the EDU discount programs at B&H Photo or Adorama if you have access to a student email. They often have better prices on the Sony FE 24-105mm f/4 G OSS Lens than the public sales.
• Be careful about buying International Version or Gray Market listings on third-party sites. They are cheaper but Sony wont honor the warranty here if it bricks during your trip.
• Use Greentoe. You basically put in a bid for the gear and authorized dealers can accept it. It is a very methodical way to get a Sony FE 35mm f/1.8 Lens brand new for used prices. I would also suggest looking at the Fred Miranda buy/sell forums. The community there is very strict about quality, so its much safer than FB Marketplace. Just make sure to check the sellers feedback rating before sending any cash over.

Building on the earlier suggestion about the summer sale window, you really should look into EDU discounts if you or anyone you know has a student email. Sony's student program through B&H or Adorama is usually much deeper than the standard public rebates, sometimes taking an extra 10-15% off the Sony Alpha 7 IV body alone. In my experience, sticking to a $3k budget for a trip requires some smart compromises on glass to keep the reliability high. I've tried many setups over the years and for a Japan trip, you want fast autofocus and weather sealing. Here is how I would play it:

• Look for B&H Open Box units (specifically Grade 9 or higher). You get the full US warranty which is vital because if that shutter or sensor fails mid-trip, you need a body that Sony USA will actually fix when you get home.
• Skip the expensive Sony GM glass for now and grab the Tamron 28-75mm f/2.8 Di III VXD G2. The technical performance is nearly identical to the first-gen Sony GM but it weighs significantly less, which your neck will thank you for after walking 20k steps in Kyoto.
• Make sure you budget for a fast card like the Sony TOUGH-G Series SDXC UHS-II 128GB. The A7IV writes 33MP files and if you're shooting bursts of the Shibuya crossing, a slow card will lock your camera up for seconds while it clears the buffer. Basically, the EDU discount plus a solid third-party lens should get you under that $3k mark with enough left over for extra batteries and maybe a nice strap. If you need help checking if a specific serial number is a US model or gray market, just let me know...

TL;DR: Purchase the Sony Alpha 7 IV Full-frame Mirrorless Camera body during the late summer rebates, but use third-party lenses to keep your $3k budget intact. Like someone mentioned, you really need to be careful with the total cost if you want high-quality glass. If you want to stay methodical about your spending before the Japan trip, I highly recommend comparing Sony to other manufacturers.

• Opt for the Tamron 28-75mm f/2.8 Di III VXD G2. It is an amazing travel lens because it is significantly lighter than Sony's options and the autofocus is extremely fast.
• Consider the Sigma 24-70mm f/2.8 DG DN Art II. This lens is fantastic and provides professional results for much less than a Sony G-Master. The Sony Alpha 7 IV Full-frame Mirrorless Camera is a beast, but buying all Sony glass will put you way over $3k. If you go with Sigma or Tamron, you'll have an extra $800-$1000 for your actual travel expenses. Definitely better to have that extra cash for your time in Tokyo!

Not 100% sure on the exact timing, but IIRC Sony usually initiates lens-specific rebates around late September. You might want to consider the thermal management limitations of 10-bit 4:2:2 recording in humid climates. I would suggest looking at certified refurbished units as a technical alternative. Just make sure to verify the warranty specs, as gray market imports wont have manufacturer support for your trip.