It sounds, from your post, as though you are worried for your relationship but at the same time very worried about what might come up in counselling. I'm guessing that you are feeling that for the last couple of years (since the last counselling) you have trodden water. You've kept the relationship together but haven't addressed the issues that took you to counselling in the first place.
All that is just guessing. I have no idea really.
My further guess is that you've reached a point, again, where you feel you can't continue in this form. The two years passage of time indicates that you two aren't able to solve the issues by yourselves. So you need something, some kind of outside input, or change, to help you.
Yes, Relate do a sliding scale. Though I'm not sure it goes much below £30. You do sound as though you're slightly resistant to counselling. That's OK, it's not going to make everything magically better. But you really are only going to get out what you put in.
My guess is that you have a very strong ambivalence about what you want. Realistically, you could carry on in your current situation for years; many do. So the question arises - what do you want counselling to do for you? And is that realistic?