There are easy ways to tell a headgasket, it will loose the coolant very quickly and will mix with the oil and vice versa, this is why you get 'Mayonaise' on the oil filler cap. Sometimes you will get alot of steam if the gasket has gone bad enough, NOT to be confused with colder weather!

1k is expensive but in any case it will be expensive for someone to do, the price comes from the labour, the gasket itself isn't that expensive.

What he ^^ said really, if it's stopped losing coolant then it's more likely to be a small leak somewhere.

As said radweld will not cure a head gasket!

A compression test could show a head gasket failure.

Martin