If you are interested in playing with spey you don't really need to buy anything to play around and see if you like it. All the casts and techniques can be easily done on your existing one handed gear, you won't easily get the same distances but you can still be quite effective. I use spey casts a lot for most every kind of fly that I do including warm water and salt water, it is more fun than over head and gives me lots more options for line control with casting, mending, and fishing. I use standard lines and one handed rods. Just think of you rod and line as a stick and a ribbon and not a fly rod and fly line and it is amazing at the stuff you can do with it. There are a lot of videos out there of guys doing it all with one handed setups.

Then if you want you can go out and buy the bigger gear.