Omron BP791IT Blood Pressure Monitor $80 w/ FSSS - New Price $74.32

Most wrist ones are pretty unreliable. we have one and it usually reads higher them actual, at least when my BP is jacked up from stress or whatever. Still better then nothing if you need to keep track to make sure your not always on the high side, or suddenly having issues. The better arm units usually are way more accurate and the one I ended up with has 2 memory settings, a guest setting, and can make PC graphs of the data collected you can print or send to your DR.
Mines a prevention DS-2200 and seems to have a stable accurate readout that more agrees with what my doc sees. The early version had problems but the newer ones have the issues fixed and I haven't had any issues other then batteries for a long time.
My Dental student at the college I go to for dental work uses a wrist version and they have several backup old school arm manual units for when there's a problem/question.
I tend to get white coat Hypertension so sometimes I'm high and they wait me out, plus I'm on a low dose of Lysinipril to keep me better under control but most times at home my readings are nice and low now, not so much at the DR's office but she now knows me and as long as I'm getting good results at home she doesn't freak out anymore
Yes your Doc should be willing to double check whatever you use in the office to make sure it's close, that's how we found out how far off the wrist one was.