Update pages/interop/estimate-costs.mdx

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

Author: krofax

pages/interop/estimate-costs.mdx

@@ -106,7 +106,7 @@ All the other gas costs are negligible.
 ## Conclusion
 
 Unless the message is *extremely* long, the cost of an interop message, taking both sides together, is unlikely to exceed *100,000* gas.
-At writing, each of gas units costs approximately $*3×10<sup>-9</sup>*, so it would take about thirty messages to add up to a full cent.
+At the time of writing, each gas unit costs approximately `$3×10^-9`, so it would take about thirty messages to add up to a full cent.
 
 ## Next steps