First class USPS mail is cheaper than media mail up to around 8 oz, and most games are 4-7 oz. Complete DS games are about 5oz, and complete 360/PS3/etc 6-7oz.
USPS parcel post is cheaper than UPS ground for something like 3 lbs or less.
If your parcel post / ground shipping ends up being more than ~$10, and fits in priority mail flat rate box, use those. It's $10.50 for a medium box, and the box itself is no longer added cost. If you buy the label from paypal, and the delivery confirmation is also free.
If it is under 13oz ship USPS. this should cover just about all single games. It travels almost as fast as priority mail and should only cost about $3.
For guides if it is over 13oz use media mail it is slow but cheaper.
Yeah, everytime you wanna ship on a budget always use USPS. USPS is backed by the federal government so their rates are lower (and they make a hole on our national deficit).