Fixing vs. Buying a New Engine / 273

I've got a stock 273 that's running low compression in one of the cylinders. I don't think anything's been changed and it's still running a 2-bbl carb. When I had it at my mechanics a couple months ago, they said it was running at about 50-60 psi, I believe, while the others were at about 120-150 psi (can't recall exact numbers). I've noticed that the car seems to vibrate at idle whether in Park or Drive but not while the car is moving, so I'm assuming that's the main problem. If it is generally how much would it cost to fix or what do you think would need to be fixed? I heard a valve job could cost north of $300. At this point would it be worth it just to get a larger running engine (318, 340, 360)? I'm also in no rush as I drive the car once every 2-3 weeks for about 10 miles a day. It still works.

On another note, surfing CL this morning. I spotted a 340 that was running (had video of it in the car) and had 484 purple cam and Edelbrock Air Gap Intake for about $1600. Is that an aggressive cam? I understand 340 are generally more expensive than 360's since there are less of them. I'm looking more for a street engine and his car looked a little pro-stock. I believe he was putting a stroker in it and that's why it was coming out.

Thanks for all your help!

First, buy the the 340.
Second, just pull the head on the bad hole and just reman it. Might cost a whole 150-250 bucks.