Quick answer
Can a spell be reversed?
A spell is never a single act. It sits at the end of a chain: the person who cast it, the system they drew on, whoever set that system's rules and whatever was agreed along the way. To undo the spell, every part of that chain has to be understood. That is what makes it hard.
Orpheus & Theseus can reverse spells. As with every consultation, the price is set after the consultant reads your inquiry, and for this kind of work it is high.
If you think a spell is working on you, start with how to tell if someone has put a spell on you, then send an inquiry.
Questions
Can I reverse a spell myself?
Only if you understand every link in the chain that created it, which is rarely possible with a spell found online or cast by someone else.
What does it cost to have a spell reversed?
The price is set after the consultant reads your inquiry, as with every consultation. For reversing a spell, expect it to be high.