What timber for edging between boundary line fence and concrete pathway?

[nvelaga]

I am planning to edge the highlighted area with timber. I am looking to suggestions on which timber to use.

Area between concrete path way and fence is 480mm. 

I am thinking to use either "200 x 50mm Treated Pine Sleeper CCA H4 - 2.4m" OR "

200 x 50mm 2.4m Sleeper H4 Treated Pine Sienna MicroPro - 2.4m" 

As both of these are 50mm , it will remove 100mm from the entire space as well as expensive. 

Is there any low cost options we have ? 

if not which one out of these two is better to use ? I think "MicroPro "