You need a bit of gold buffer. When you're above a certain pricetag, when you have a x1 match spree, you start losing money. But - when you have a winning spree, you get more.
With a few days of playing, I find that heavy crossbow, 1x steel bolts, mail with surcoat, spiked helm, mail chausses, mail mittens, glaive - totalling circa 30K - is not only upkeepable but makes money. I think I could easily afford circa 5K more gear and break even. All in all, I think 35K is a reasonable amount.
Of course, people like Tai who occasionally play as peasants get to upkeep more when they're not playing lolstab peasant role ;)