mailee, if your timber costs alone are ~$567 I'd expect your mark up on that to be a minimum of 25% = £142. It probably ought to be higher than 25%. After all, how much time and effort do you have to go to to source the material, and then you have to go and pick it up too, which is about how much your time is worth and what your vehicle costs are.
You mention that on top of that there are other expenses such as hardware-- let's say a cost to you of £40, plus your time and vehicle costs again to pick it all up, so mark these up as well at say 25% = £10, which probably will cause you to lose money.
So if we add up your material costs and mark-ups we have, 567 + 142 + 40 + 10 = £759:- your charge for materials to the customer. Incidentally, £567 would get you about 19ft³ of air dried oak at a higher end price of £30/ft³ including VAT. Typically there's a 125% waste factor for air dried, waney edged oak. The waste factor I use for kiln dried square edged english oak is 80%, but you won't be using this for exterior gates.
Your final charge to the client you reckon is going to be £1132. Subtract from this the charges we already know about, i.e., £759 and you're left with £364. Your profit for the labour element and delivery of the completed gates has to come out of this. At a pretty standard sort of rate for joinery work of £30 an hour you need to be able to build and deliver the gates in about 12 hours hrs.. Installation would be a separate job.
Unfortunately I suspect you're a bit on the light side with your prices if you are trying to make a living at this kind of work. However, if this is a new venture for you and a learning experience, or you're only working this kind of job as a sideline perhaps a return that small is okay.
Mind you, processing 19 ft³ of rough sawn oak alone to get it basically square so you can do something useful with it is a **** of a lot of work, ha, ha. On the other hand maybe your price for the oak is a machined PAR price meaning there's much less wood to handle. Slainte.