There are ways to get the finish, block out the part and leave 0.5mm on for final cut then clean up all the chips and do a final full depth pass to remove the 0.5mm.

I used to do this on a large CNC mill than has speed and feed limitations and got good surface finish. Personally I have found that the slower you cut plastic the better the finish because at high speed it just wants to melt.

Can you afford to go up to a larger machine like a 6040, these have ball screws and a choice of high speed spindle.