Definitely buy a monitor--they're not that expensive. If it is white coat syndrome, you may go along way to fixing it if you are reassured that your readings are OK at home. Just make sure to use the right size cuff and take it according to the rules...things like where your arm is relative to your heart makes a difference. I have a meter at home because I've flirted with borderline blood pressures, and it's been a very useful tool for helping me figure out what spikes it and what doesn't.
Your doctor may also be less likely to push meds if you can assure him that all readings at home are normal.