Planning a wedding in six months is not something impossible. It surely does require considerable planning to make it feasible but on the overall, with some dedication, you would ultimately get there.
For a last minute venue, you can opt for a public park which would pose availability and booking issue. But you might be needing some permit to carry out a ceremony in a public place. You can also ask a close relative such as your parents the permission to host your ceremony at their place. Someone with a huge garden or gorgeous lawn might be willing to accommodate your ceremony. You would have to gift the person and provide for a cleaning crew to show your gratitude.
A short amount of time is not a hindrance to choosing the perfect dress. Normally a custom-made dress might be made in under three months but the price would be a bit hefty. You might think about wearing your mom’s wedding dress or getting one from a thrift store.
Securing a place on the list of a “celebrity baker” might take a while. You might opt for a local baker and pay a percentage of the price as deposit in order to book the person. If the traditional three-tiered cake is not possible you might go for a smaller cake and serve other desserts such as French macarons or small genoise cakes.
If you live in the US, you could get great last minute honeymoon deals in the Caribbean. You could also consider islands such as Nantucket, Block Island or Kiawah Island.