Sadly, I don't think we'll be seeing any tamiya paints for a while (I liked the candy green they had). My LHS still has some tamiya paints, but his supply is getting low and hasen't seen anything from them (including the primers) since March. IIRC, one HS I went to a while back had a few cans left for around 15-20 bucks!! (Yikes!)
I'd suggest looking for an good alternitive primer if paying $20-30 a pop for tamiya primer isn't for you, or your wallet. (if it is and you gotta have it, then go ahead)
I've heard many people had great results from Dupicolor, Plastikote, and (some) Rustoluem primers. But if you're on a tight paint budget and looking for very cheap good alternitives (though the latter ones arent so much, but in more units the $$$ adds up). I use Sears "Quick & Easy" Gray primer. It works very well over bare styrene, sprays on nicely and drys quick & smooth (almost no sanding needed); cheap ($1.70 for a 12oz can) and easy to get at yer nearest K-mart or Sears Hardware store. They also had white and red primers, which are no longer being produced anymore (sniff, sniff... I really liked them too). But Flat White (I use the colorplace brand, which works very well) works as a bright basecoat for gloss white, yellows, reds, blues and so on/
If you like it, you can stock up on 12 cans that will last you a long way for less than $16! which is the price of Tamiya primer if you can find it.