Depending on what version mobo you're looking at, the 1mb Chip RAM mod is relatively easy to perform. Cut a trace and solder a couple of pads together is pretty much it. Lots of info online if you search for it.
To bring it up to the full 2mb of Chip RAM, you'd need a DKB MegaChip or equiv. I have one for sale under the same user name, but I think AmigaKit still stocks a new one for a little less money. Nice thing about mine though is that you don't have to remove the Gary chip to sneak another socket under and Agnus is socketed. I realize mine might be priced a little "high", but figure I may as well keep it for anything less. Especially after ePay, ScamPal and the post office all get their cut.