As above, please don't shell out on something-you shouldn't have to pay to essentially do your job. I know many buy little bits and pieces (I do 
) but it shouldn't be necessary.
When I say I buy bits, I mean, for example, the other year I was in Aldi and spotted a pack of 20 highlighters for £2. I bought those and to be fair, I have used them loads. That's about my limit though.
What is the school feedback policy? You may not have had it yet so if not, hang fire until you see it.
We have just updated ours and are very much in favour of giving feedback that is meaningful and moves pupils forward but isn't onerous. Verbal feedback is acceptable and doesn't have to be stamped/signed.
For instance, I teach Science (including A-level) and do a lot of feedback in lessons. Either whole class e.g. if going through calculations or as I am circulating the room while pupils are working (all being well, we can do that again in September). So, I may see a child struggling and I will sit with them, re-explaining and modelling straight on to their book or perhaps giving a hint or two and then they complete the task. Similar if I want to challenge a pupil further.
It will depend on your school policy though 