Leaking S10 Radiator...big trouble to replace?

A whole lot if it isn't fixed soon, I guarantee it will catch you at a place you don't want to be pulled home from, in just a matter of time. By the way its not too much trouble to change if you are a little mechanically inclined.

Depends on whether you want to buy a new or used a salvage yard will cost significantly less. As far as changing the radiator is concerned is a fairly easy task, you will need a catch basin to capture the anti-freeze.
On the core support are three bolts removed them as well as the fan guard three bolts each side, you'll need a pair of pliers and a flat head screwdriver As well as a few wrenches, with the pan under the bottom hose squeeze together the clamp and slide it down the hose if you cannot pull the bottom hose off by hand use your screwdriver on the inside of the hose to help loosen it up then you should be able to get it off, then remove the two lines for the transmission it will leak some and I suggest using a rag under that then remove the top hose to the radiator remove old radiator and install the new radiator ..reverse installation is how it is reinstalled as well as replace fluid {anti freeze / dex cool } with the engine running add fluid as needed then replace cap and tighten .

Trouble is a relative word on these. If you have a manual transmission, then you're easier off. An automatic has cooling lines going through it for the transmission, and make for having to catch one more liquid. As for the rest of it, you can probably pick up a radiator for about $150 worst case scenario. As for changing them, you'll need to remove the fan shroud, and the radiator mounting fasteners, drain the radiator, and if you have air conditioning, you'll have to deal with that as well. It's easiest to remove the fan and fan clutch as well, as it'll give you more room to work. You'll want to get radiator hoses as well, and it's a good idea to do the thermostat at the same time. All in all, you're looking at about $250 in parts if you do it yourself, and a few hours of toil. It's not a difficult job, it just takes a little time and patience.

if the coolant gets low enough the engine will overheat, so your only option is to pull the radiator to see if the leak is repairable. most radiators now have plastic side tanks and if the tank is cracked or the seam where the tank is crimped to the radiator core is leaking, you wiil need a new radiator. many of the aftermarket radiators have lifetime warranties.