I suspect eBay will probably meet your needs. Before going to Ireland this past June, I bought an unlocked GSM cell phone (but not a smartphone) for $19.99. I didn't check prices on low-end smartphones, but I'd guess that some reliable vendors are selling unlocked GSM smartphones for less than $100.00. As with most eBay purchases, it's probably wise to check the seller ratings as well as the price before buying.