Part of the decision on whether to self insure might be determined by what your vets are like in your vicinity. I know that around my way I would be hard pressed to find a vet that I would regard as sensibly priced and responsible, what I would term a good old style east end vets. Instead, we have some expensive vets whose premises are geared to making the customers feel that their pets are being given a superior treatment. (Goddards, I'm looking at you)
You will quickly get to know local dog owners, talk to them, ask them what they do and then make your decision - there's absolutely no rush. Another consideration is that you will be getting what I would describe as a robust dog, as far as I know border collies the breed have no significant weaknesses, like hip dysplasia, as they are bred for qualities other than appearance. The cross bit adds a bit of uncertainty, I wouldn't know how to evaluate it, but generally crossbreeds are less susceptible to problems.
I confess I never insured any animal, but I have looked at it closely in the past and been singularly unimpressed with most offerings I saw. The question you need to ask yourself is, were you to be in the position of needing it, could you afford the vets treatment if you had to? If you couldn't then insurance adds some peace of mind and is to be recommended, as if circumstances arose you would either move heaven and earth for your pet, or blame yourself. If you can afford, you are then free to consider whether to take the risk yourself.