I would urge you not to buy as it sounds you already have a bias. Yes, its expensive. Having done it I think it would cost more to do the R&D yourself to get it done to that level of correctness. Also because you are talking about Guns and moving vehicles I see it as an insurance and liability asset to buy from a seperate company. The renfaire I work for cant build a playground because they cant insure it, but if they purchase one they can because their is a liability sponge.
I had a high actor turnover because we made a few poor choices reguarding the guns and the armor- the learning curve was high- part of what you are paying for is the learning curve you are skipping by buying from a vendor.
I respect your choice and fully understand it- if you cant afford to market any attraction then you shouldnt invest to much in it.