Pretty cheap 512MB chips...

[Benn]

OWC currently has the following:
512mb PC100 CL2 Low Profile SO-DIMM for PowerBook G4 Titanium 400MHz  
and 500MHz models only(Not for 550-667Mhz models which do require  
PC133!), allows up to 1GB! Lifetime Warranty. **LIMITED AVAIL CLEARANCE  
ITEM!** (OWC100SO512328S)
$55 -  
https://eshop.macsales.com/AddToBasket.cfm?ID=4147&Item=OWC100SO512328S

512MB PC133 CL3/PC100 CL2 LowProfile SO-DIMM(Stacked) for PowerBook G4  
(all models 400MHz-800MHz, iMac G4. Allows up to 1GB total possible.  
LifeTime Warranty! (LIMITED SUPPLY CLEARANCE) (OWC133SO512328S)
$60 -  
https://eshop.macsales.com/Catalog_Item.cfm?ID=3971&Item=OWC133SO512328S

If I recall correctly, these are the cheapest prices I've seen on  
either of these modules.  If I weren't going to buy a 17" powerbook,  
I'd get one of them myself.

Benn