So, having said all that, MY OPINION on what to buy and in what order goes...
Scope/Mount - Your current scope will be fine so a solid mount is in order.
Camera - What you want to image will affect your choices here. Planetary is easily done with a webcam, DSOs respond well to CCD and a DSLR is sort of 'halfway'.
***This is the minimum equipment, from here you can step up slowly (or quickly) as you learn what everything does and whether or not you need it***
Software - What camera you choose will give you software options, Canon DSLRs (for example) allow you to use Backyard EOS or AstroPhotographyTool to control them completely from a laptop. This also includes processing software like DeepSkyStacker, Registax, Irfanview, Photoshop...
Collimator - (some would say you should already have one) Once you start to get recognizable images you will undoubtedly start to nitpick, the first source of error is bad collimation. (Do your research on these)
Coma Corrector - This will correct the 'smeary' stars around the edge of your images. (You can see it in my M42 image because I don't have one)
Autoguider - Whether you decide to go with a seperate Guidescope or Off-Axis guider it's important to get a decent camera. I have the Orion StarShoot Autoguider, purely because it came up at the right time at the right price. It's the same as the QHY5 but with more restrictive firmware, so the QHY5 will work as an imaging camera and the SSAG won't.
I would say this is the 'base' level of Amateur Imaging, from here it depends on what you plan on imaging but that covers the basics and allows you to get used to the gear you have before adding to the learning curve. For example a more sensitive monochrome camera, RGB filters, Narrowband filters, filter wheel... Like Robert said, you can spend $2k or $10k
