A radiator replacement is not technically difficult and something that an
independent shop should be able to do without any problems for less money.
I would get the quote in writing and then ask an independent shop that has
ASE certified technicians for a quote.  If you are not in a hurry, the
radiator could be sent to a radiator shop for re-coring, depending on where
the leak is.

It seems a little strange to me that (since you don't indicate you've had to
refill the radiator because of this leak) that they've suddenly found a leak
in it.   I'd want to have a good hard look at the  radiator before
authorizing them to replace it.  I'd also check around and find out
competing quotes for replacing it if necessary.
Not necessarily related, but years ago I had a Peugeot which had a faulty
head gasket allowing coolant into the engine, and making an emulsion of the
oil.   The only available Peugeot mechanic wanted about $1200 to replace the
head gasket (and was quite surly to boot, making it a "take it or leave it"
deal) so I went home, got a bottle of black gook called "radiator
stop-leak", poured the stuff in and changed the oil, and drove it without
problems for a year or more before I sold it, still with the repaired gasket
doing its job.   Try it out.  It may be $5 well spent.

A perfectly decent non-Toyota new replacement radiator can be had for
$200-300. As for the replacement labour ... lets see what has to be done.
- drain the current radiator            5 minutes
- remove the existing rad hoses    10 minutes
- remove the clips that hold the rad in place    10 minutes
- remove the old rad and drop the new one in place    1 minute
- replace the clips and rad hoses 15 minutes
- fill the rad with new coolant, and blead the air out of the system    15
minutes

I make this 56 minutes, buts lets make it 1.5 hours to allow for goof ups
and profit margin. So, 1.5 h at $50 / hour = $75.   I'd ask the dealer
explain exactly what the other $235 labour is supposed to be for.

SD

AutoZone:
SPI         CU1409        LLT              $148.99

Looks like a decent price to me! Probably good for 30,000-75,000 miles or
more, if you do regular service on your cooling system.

Oh, btw, as Ray says, it's not a hard job. Not hard at all, In fact, all
it requires is a 10mm wrench, a screwdriver and a pair of pliers. Maybe
take half an hour if you can spin a wrench, 75 minutes if you can't...

I had it replaced on my '93 Corolla 1.6 XLI a few weeks ago, they asked
about €180 ($240) for the radiator and then something for labor, I'm
pretty sure that was below €100 ($130).

My repairshop told me just like you that they can't patch it.

Hans

It's an easy job to do yourself, or take the rebuilt one from Autozone
down to the local high school, give it to the automotive shop teacher
(assuming they have one) and let the class do it.  Or find some kid in
your neighborhood who likes to work on cars and give him 50 bucks to do
it.  That price you were quoted is a total rip-off.