The time it takes to launch apps should drop from a minute to a few seconds.SSDs start at about 0 for a decent-size one (120GB), with 250-256GB and 480-512GB drives going for a few hundred dollars more.
Your computer's workload is compounded when you don't close tabs in your browser and you end up with 150 open tabs at once.
Even if you have to "throw away" your existing desktop memory because of a shortage of slots, 8GB of memory shouldn't cost more than $50-70.
Installing an SSD is like installing any new hard drive: Find a free SATA port on the motherboard, connect the SATA data and power cables to the new drive, secure the drive in a free drive bay, and install the operating system on it.
An SSD is so small that you can slip it into any drive bay with an adapter, even the one that was made to hold floppy drives.
When you bought your current desktop a few years ago it seemed like the fastest thing, especially compared with the PC it replaced. Does your PC start out fine but slows down once you've been using it for a while?