Welcome to NeuroTalk!

I think you would do better on oral supplements. Injections only stay in the blood for 72 hrs. The rest of the time, there is nothing.

I have a B12 thread at PN here:
http://neurotalk.psychcentral.com/thread85103.html

It gives MEDICAL links, and I try to explain how to use B12 successfully. (with little stress on you, or your budget)

Studies show oral B12 works...but I suggest you take it carefully
on an empty stomach so it can be passively absorbed correctly.
Most doctors do not know this, but it is explained in the link to AAFP I gave above.

You are not terribly low, as 400-500 is the cut off for treatment.
But to see faster results I'd suggest you take 5mg (5000mcg) daily on an empty stomach, for 3 months. And then get retested.
This will be easier than shots. The body then can take the B12 in a daily manner, and send it where it needs to go. Some has to be absorbed by the CSF (cerebrospinal fluid) and also stored in the liver. The seesaw feelings of nothing between shots should disappear as you take your oral B12 daily.

If you come up to over 1000 using the oral, you can continue with the 5mg (it it not harmful) or you can go down to 1mg a day.
Most of us use methylcobalamin form, which is the active form of B12. The injections use cyano...and some people can't convert the cyanide portion well. Since Methyl is the form your body needs, taking it directly is more successful. We are talking pennies a day for you in cost. Most of us use an online source, iherb.com or vitacost. Methyl is not commonly in local stores, but it is appearing some now.

That thread I gave you has at the end, information about a new dosage form of B12 coming soon. I don't know if it is available yet, or if it is methyl, but it looks promising. (and will probably be more expensive).