A leak down gage is positive pressure based on a hundred pounds psi, it has 2 gages - 'befor' and 'after' - so you can read the pressure loss between the gages. A vacuum gage is different, it has a single gage that reads negative pressure. As far as a 'good' one? i'm happy with just about anybodies vacuum gage, that isn't a scientific reading and i think of it as relative. For instance, if you set timing using a vacuum gage you would adjust your timing to the highest possible vacuum. It makes little difference if you use an inexpensive gage that might be off by a 1/2" of pressure or a scientifically calibrated instrument that is certified - you are reading to the highest pressure. As far as a leadown tester, they'll set you back. I have one from Moroso. I don't think there is an inexpensive leadown tester, all of them are well made - just be sure to get the one with 2 gages.
What he said...^^^ The OTC leakdown tester is pretty decent as well. Any good one will set you back around $95- 100 or so....lesser ones are not that great, and you don't need a $500 one. You actually can build your own leakdown tester; however, with the increased prices in metals, and therefore fittings, you'll only save about $20-30 bucks.
as far as leak down testers go you can make one with a 60 psi gauge, a regulator and a few fittings and Milton couplers. set the gauge to 60 psi..plug it into a hose run to the spark plug hole...reading the gauge backward from 60, 30 psi would be 50% leakage, 45 would be 25% etc. build it yourself, all your doing is putting a set amount of air in the cylinder and recording where and how much the cylinder is leaking. It's not rocket surgery.
IF you have a bad problem you can hear it at the exhaust, carb or breather, that and a comp. check should point up where the problem is.
Continuing on from Rug Blasters, post i made something up kind similar pretty much for free. Smashed the insulator off an old spark plug and welded a pcl airline fitting to it. Set the airline pressure to 100psi and used my tire inflator with integral gauge on the pcl fitting, it fitted pretty good. Not a perfect solution but it helped me eliminate thoughts of busted rings etc as each cylinder held up well. Chris
Harbor Freight has a Leakdown test kit that is fair quality and inexpensive. It has everything you need.
Hit up some pawn shops in your area. Snap on tools makes the best of each. Also look at the Sears tool catalog. You can order good quality tools thru them.