You crazy? **** no! The people who are crazy are the ones saying you can't have fun for buying a go kart!
Ok, you want a easy to get into, big tire cruiser that can get up light hills.
Well just make sure you want a kart because an ATV will fit this category for getting into a bit better as one foot over and the straddle seat would probably be easier for you to get into.
Ok, fine, say you don't want an ATV. You are probably going to want to look into a late-90s to early '00s off-road suspension kart. They are usually quite a few inches off the ground compared to butt on the ground yardkarts. Yerf-dog and Mancos are good ones, but there are many brands. You can get a rolling frame for ~100$ if you look around. Look for ones with 5-6HP motors. They will be the cheapest to work on. (100$ for a 6.5HP motor vs 300$ for a 13HP motor)
Now you said you were around 280. That means we're talking around 400 loaded weight. Combined with small hill climbing, a Torque Converter(type of go kart automatic clutch and transmission in one) is in order. You can get a clone one on eBay for 50-60$ given the rolling frame you buy doesn't come with one(if you get a rolling frame with a dead motor, it will have the T/C).
Now if you buy a rolling frame, you will need a motor. There is no question here, the Predator 212. 5 bolts, a throttle cable, and in about an hour the engine should be in and installed ready to go. 100$ with a coupon for this puppy.
Depending on the roller frame you get, it will likely need a seat and maybe a throttle cable or something. Probably will be some guys kart he bought 20 years ago and sat under a tree for 15 of those 20 years. Add 70$ for all this crap.
Tires? Whatever it came with is fine. Likely it will be setup with 15" in the front and 18" in the back or 16" in the front and 22" in the back.
Ok...so we've put in around 330$. Now you have almost 2 other Benjamin's to do whatever you want to do with. This is practically worst case scenario. I put in around 210$ for my Manco kart and it is great.
These karts should go around 32mph max speed, so a good cruise around 25mph is no problem for these.
Get on Craigslist, you got some shopping to do.