If you have a limited amount on your budget i would suggest sticking with your stock wheels and going to a narrow 33 or 34" tire. Tirerack.com will get you started on some tire ideas. If you decide to go larger (35" or higher) you may want to go with the leveling kit as mentioned. Be aware there is more to just adding tires wheels and lift/level kit. To do all of this correctly and properly you could easily be into $2500 and up. Include wheel/tire, lift, mounting, balancing, alignment, installation etc.. If you do all this you will probably want or need to purchase new/performance shocks, stabilizer, possibly track bar etc...

Seeing as you have the 250 and decide to go with a leveling kit (2.5" for example) you may realize you will want/need to lift the rear to level the truck resulting obviously in additional costs.

Set goals for the truck that you want and take your time to research all the possibilities and options. Purchase the items you decide on in intervals until you have what you want. You will loose performance and economy period. That is the price you pay for modifying it. Additional costs will be involved to recoup the performance but your economy will typically never return.

If you really need tires now, purchase some new stock or 275/285 tires and in the meantime do your homework.