For you since you are on a budget I highly recommend Blue Microphones Bluebird is has a list of $499 and around $400 street price if you fanagle at bit with the sales guy..
No it's not a tube mic but the sound is quite respectable and has the perfect curve for vocal. Comes with a suspension mount and pop filter in a nice wood box.

As Far as tube Pre Amps Go .. you get what you pay for.
Cheap pres don't really add much except a lot of hype.
However a great pre amp will change the sound dramatically
Such as a Universal Audio LA 610. Or a Blue Mics Robbie but they both come with a price attached.

Thier is only one tube mic in the price range you mentioned made by a company called Sterling model ST66 it has a good sound but not a knock you over sound. Of course I have no idea what are you are useing at this moment to record with. If you are using a Shure SM58 to record with then the ST66 will blow it into the weeds in one vocal line.
List $699 but can be had for $399.00 just about everywhere.

Let your ears decide... ultimately it is what your happy with and will do the job for you. But again I must warn you.
You won't know what you are missing until you actually hear it against the next level up. It's Kinda like compareing a Ford to a BMW and then compareing the BMW to a Ferrari

Please Do not expect it to sound like a $2,000 Neumann TLM 49 if you put it up against a microphone of this caliber your ears will be amazed but it's incrediable magical qualities come with a price.

hope this helps

Larry Read 40 year veteran of the Music Industry

your only a stranger once after that a new found friend
http://cdbaby.com/cd/larryread
http://www.LarryReadsMusic.com
Singer/Songwriter/Guitarist/Audio Engineer BMI &
Audio Engineering Society Member