Removing a transmission is a job worth doing yourself if you have the tools and a good place to work on.
When you remove a transmission it can seem like a daunting job although it can be pretty easy in most cases, but if it's your first time it may take longer to remove it.
The actual time it takes to remove the transmission will depend on the vehicle as some vehicle like on certain trucks or vans, the transmission can be very easy to remove by just disconnecting the drive shaft, unbolting the transmission from the engine and unbolting the torque converter from the flex plate and unbolting the transmission from the crossmember.
Although on some vehicles like mini vans, cars etc that are front wheel drive, the transmission can be very difficult to remove and sometimes not worth it.
I've removed and installed a few transmissions in trucks and in rear wheel drive vans and they were actually pretty simple and I can often remove the transmission in a day of slowly working and then reinstall the other transmission the next day.
It can save you thousands in labor charges if you can remove and reinstall the transmission yourself.
But it's also best to have a transmission jack and a good concrete surface to work on so that the transmission jack can easily roll on.
If you don't have the tools or place to do it or the time, it can be best to pay someone else to remove and install the transmission.
But if you're not in a hurry, you can pace yourself and learn along the way, even through YouTube videos for your specific vehicle.