Replacement headlight for 1980 GS450s

[apopleptic]

So while I was riding on the highway the other night, my headlight blew out. Immediately flipped to the highbeam, but boy was it startling.
Now my local shop can no longer seem to find me a bulb, and the advanced auto says they can't either.
Seems like the bulb it 6.25 inches in diameter and all they have are 5.75" and 7"
I looked around and everyone seems to be charging $50~60 for just the bulb which is rediculous. Does anyone have any insight? recommendations on an upgrade? Suggestions on a new housing that isn't to expensive and won't require many other changes to the bike? I was thinking it would be nice if it still fits the stock windscreen, but if it doesn't I'll just end up selling the windscreen to someone who wants to restore their bike to stock (S) condition.
I really want to keep this as budget friendly as possible, my income is still very low at this time...
Thanks!

[barnbiketom]

http://www.ebay.com/itm/BLACK-h4-halogen-headlight-cafe-racer-clubman-cb350-12v-7-lens-honda-yamaha-/120984699957?pt=Motorcycles_Parts_Accessories&hash=item1c2b400435&vxp=mtr

This has the replacable H4 bulb. this seller has different ones than this so click on their 'other items'
My other GS450 had a similar lite and it was appreciably brighter and if it would ever go out, replacement bulbs are like 6.99 anyplace!!!
It was 35/50 Watts too so no additional drain on the already weak charging system either!!!!