Honda - Stick - Trouble Shifting

I have an old honda civic (manual). I have trouble putting the gear in to first, second and third gear at times. It just won’t go in sometimes and sometimes it is fine.

Any ideas on what this might be and the cost?

Could be a master or slave hydraulic problem. If it were at matter of replacing one of those the cost wouldn’t be bad. Your clutch could be worn out, that would be more expensive to replace. The third option is that problem is in the transmission which would be the most expensive option. I’d start by looking for a hydraulic solution first.