How much would it cost to fill in my hairline? (photos)

Your hairline looks natural and dense.  I do not think grafting into this hairline is going to do anything but make it look unnatural.

A great first step would be an online consultation. Often you can submit photos to top hair restoration surgeons for a complimentary evaluation. This should help lead you in the right direction. Having multiple consultations with different doctors cannot hurt. 

Also; information such as your family hairloss history as well as your preventative regimen that you are on such as minoxidil use and other topicals would be helpful.

It appears you have a nice hairline so I do not expect you to require a great deal of hair which would translate into a lower price. It is best to have an in-office examination to determine exactly how many hairs you will need based off how you would like your hairline designed. You can also call for price ranges for a better estimate. Hope this helps!
Johnson C. Lee, MD
Board-Certified Plastic Surgeon
IG: @drjohnsonlee

It would cost approximately $4900 to give you the density and natural look you are seeking. Check out our website for photos, etc: gulfcoasthairrestoration.com in New Orleans

Hair transplant can be an option for forehead reduction,  correcting  receding hair line and asymmetry on your frontal hair line/forelock. But I do not advice you have a FUE, because of a chance of loosing the natural look.  If you wish  you would get the desired hairline in just one session of dense packing hair transplant with  600-700 grafts  with FUE.. 

AS you are in Los Angeles, you should visit us and get an assessment. This Saturday, we have our monthly open house where you can see many patients who had it done and get a free consultation at the same time  Call for time and address