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Paying for solar isn't just costed the raw components. You need to consider permit applications, all the rails, mounts, cabling, grounding cables, clips, combiner boxes, surge arrestor, cable ties, properly sized cables, MCBs, isolators, DB boxes and then the scaffolding, HSE equipment, labour and insurances etc etc etc. Balance of system costs isn't just exactly x components but x+10-20% because of possible defects or breakage while installing etc. Then businesses need to not just make money but factor in warranties (remember they are slaved to you for at least a year). Plus if you intend to have this as grid-tied, you also need to pay a qualified professional to certify the roof structure AND the electrical installations. Once you take into account all this, then make comparisons to the quotes you receive. Only then will you know if its expensive or not. Just some food for thought.