Only you can decide where your money is best spent but if your use of the bike involves putting it at risk of theft, I would not be spending big bucks on it as it will increase the desire to steal it considerably. If you've got $4-5k into a bike, you're not going to want it out of your sight for a second and if that is going to effect how you want to use the bike, then it's a bad idea.
If 20km/5 days a week is what you plan to do, I don't think I'd spend any more than a grand on the complete bike but that is just me. If you have the means, get what makes you happy.