Fiancé's Octoberfest/Zürich/beyond? 30th bday, help!!!

checking out Zürich since it's so close and I hear it's beautiful.

Wrong. It is along way from Munich to Zürich, it is a slow train route and often a bus is faster (rail route currently being upgraded)
It is a nice city, but there are nicer, and most people go to Switzerland for mountains, not cities.
And anywhere in Switzerland is more expensive than Germany, you said you were on a budget.

If you decide to do Switzerland as well.

1) Fly into Munich and out of Zürich, saves doubling back.

2) Instead of Zürich spend a few nights in Luzern.

• Luzern has a lovely old town, and it is on a lake. You can wander around the old town (you can't afford to buy much)
• 360° view of Luzern: http://tour.luzern.com/360/en/
• Some photos: https://www.shutterstock.com/search/luzern
• You can take boat trips on the lake. The far end of the lake is fjord-like with vertical sides: https://www.lakelucerne.ch/en/
• And there are three local mountains you can take trains or cable cars up (Rigi, Pilatus and Titlis). Titlis has a glacier at the top. See here: https://www.titlis.ch/en/adventure?c=60692

All this will be expensive. Cheaper to stay in Munich and do a day trip to Salzburg.

Are you talking Oktoberfest 2019 or 2020 ?
Checking our favorite Munich hotel, lowest price for 3 nights (M-Th) in early September is €200; the same nights in late September it's over €600. And this is in a hotel far outside city center. (Price is for a bath-down-the-hall double, non-refundable; free cancellation and/or en suite bath are more.)
Booking.com shows that many places are fully booked or have only a few rooms available. Oktoberfest is a very popular period.
Some people train on from as far away as Salzburg (2 hours by train), which is a destination in its own -- similar room in Salzburg would be €400.

If this is for 2019, and I presume it is since you're talking about a current house remodel, this is going to be problematic.

For starters, scratch Switzerland. It's incredibly expensive and you said you're on a tight budget. Save it for when you can spend more. Perhaps enjoy the Alps in Germany or Austria instead, there are good values to be found there.

Secondly, it is very late to be planning a trip to Oktoberfest this year if you wanted to stay in Munich. If you MUST do Oktoberfest, I'd stay well outside Munich (perhaps others here can give advice on a charming area that's far enough away to not be impacted by the high rates during the fest) and take the train in for the day.

Another option would be going to another bierfest. Stuttgart's Volksfest is nearly as large as Oktoberfest, and very similar, but does not attract as high prices or international tourists, so it can be done relatively on a budget, and you could stay in town, although Stuttgart is expensive for hotels year-round - I'd consider an AirBnB or staying in a nearby charming town with good suburban rail to the fest grounds - Esslingen am Neckar would fit the bill.

This is a hard nut to crack. I am not familiar with Flixbus fares or details, but maybe a 2-2.5 hour bus fair to Mittenwald from Munich ZOB? There are a lot of apartments for rent in Mittenwald and maybe you can keep it under euro 60 a night with breakfast? Mittenwald would put you in the mountains and a famous touristic town. You could eat cheap at Butcher shops and Bakeries. Splurge for a euro 50 dinner? Hike when not at the Octoberfest and commute on local buses and train (Garmish etc)? You could do the Karwindlebahn, but it is not cheap at euro 29,50 per Adult.

If you must go to Switzerland, I would go to Luzern instead of Zurich, but anywhere in Switzerland is expensive and you don't have much time. Staying in Germany or including Salzburg, Austria makes more sense. This late in the game everything is going to be more expensive (plane fares, hotels, etc.).

To echo the above Switzerland and Octoberfest are not budget friendly

I was thinking maybe two days in Munich for the Octoberfest and checking out Zürich since it's so close and I hear it's beautiful ... Total time available for us to take off work = 6 business days + weekends

Like other's said forget about Zürich as it is too far. With the limited time I would suggest Munich and one other location not more than three hours by train form Munich. Innsbruck (and other locations in Austria) would give you a feel for the Alps if that is what you were looking for.

Budget = I need every dollar to go as far as possible

Accommodations = I don't plan on being indoors much so I'm open to staying just about anywhere

Time frame = Anytime that fits into Octoberfest schedule, even if it's flying in earlier or leaving late so long as we get a few days there.

As has already been said, you are very late in planning a trip to Oktoberfest and most reasonable accommodations in the city will be booked, however you are in luck as as Motel One is opening a new hotel in Haidhausen just in time for Oktoberfest and they seem to still have first weekend plus the full second week available for 179€/night with no breakfast. This is probably your best bet on short notice. If this is still too steep for you then I would suggest looking at places around Tegernsee and taking the BOB train into town (about 1hr). Rooms should be around 100€/night. Serach this forum for Tegernsee to see why I recommend this area.

DJ