A Slot-In filter kit will normally consist of (working from the end of your lens) the following:
I will use Lee system as an example because I have one, though Hitech also have 100mm system as well.
1) A
77mm Adapter Ring - Wide Angle (for 11mm). This screws onto the end of your lens where any normal filter would be attached. £33
2) A
Lee Holder Foundation Kit . This attaches to the Adapter ring, by pulling out the pin/knob then releasing it and is very easy to put on and off and is secure. These hold 100mm filters which just slot in. £48
3) A ND filter or a set of ND Filters. I use
Hitech rather than
Lee (half the price). Choose soft or hard edge. Hard is good for seascapes, soft better for more rugged landscape. Or get a reverse grad for sunsets. I bought a set of 3: 0.3, 0.6, 0.9 ND's 1, 2 and 3 stops, but on the whole I mainly just use the 0.6 (2 stop) filter 90% of the time. A set of 3 is £79 a single ND is £35 a reverse ND £60
4) If you want to use a Circular Polariser in front of any ND Grads, or just on its own but mounted on the Lee holder then you then need a
Lee Filter 105mm Front Ring £27 (you can also buy it with a foundation kit a bit cheaper I think) and a either a
Lee Filter Glass 105mm Screw in Circular Polariser £225 or a slightly cheaper
Helipan 105mm CP £175
I think all prices I quoted are excluding VAT (except the Heliopan) so add 20%
As you can see, adding the CP option makes it much more expensive, alternatively if you don't need to use ND Grads with a CP, just get a relatively cheap screw in CP separately.
If you just want a Lee Slot in Filter system on a wide angled adapter and 1 Hitech 0.6 ND grad its going to cost you about £120 + VAT.
I got no vignetting on mine in front of a Canon 10-22mm on a 1.6 crop sensor, and none on a 17-40mm on 5DII full frame.
