The two common ways to hook a T5 to a 302 are - with an adapter plate between the T5 and an original bellhousing, or just using a 5.0L bellhousing. The plate option allows the factory linkage to be used if you want to keep originality, and the 5.0L bell option allows the use of cable or hydraulic setups. Many consider the cable, and especially the hydro conversion worthwhile. Both increase the cost and labor of the swap.
So, other requirements common to both aside (X-member mods, shifter and placement. possible tunnel mods, etc.) the bottom-line is that the adapter plate is rather expensive for what it is, but you need little else to do the swap. 5.0L bellhousings are dirt cheap, but the cost savings is offset somewhat by the cable/hydro conversion. You can see why there are proponents of both options.