Keep it up!
I do hope you meant to type '6/7mm' as if the pins are that many centimetres apart they are a waste of time. I expect you have made the correctly.
Yes there are lots of things that can keep beekeeping costs to a minimum, or at least reduce the costs by a reasonable amount.
Apart from my original beesuit, smoker, gloves, hive tool, a super with frames (in my first year) and a 14 x12 brood box (possibly), nearly everything else, where appropriate, has been obtained as seconds or sales items, made, or an alternative used - rather than the high-cost first-quality retailed items.
The cost of investment in tools may seem steep, at first, but they can be used for other purposes, as confidence grows in DIY. I already had the tools, or most of them, anyway.
The one area which is difficult is that of polyhives - an injection moulding machine, ancilliaries and moulds are just too expensive for any DIYer on an economic basis!! But the good ones are likely to last 30years or more, so not too bad - and they are very competitive, in price, with wood hives.
With one colony, simple replacement with new frames is likely cheapest, but when on multiple colonies, wax recovery, re-use of frames and generally recycling becomes an effective and cheaper option.
I am considering using potassium hydroxide (more expensive than either sodium hydroxide or washing soda) for frame cleaning next time as the effluent can be diluted and sprayed over the garden as a useful fertiliser - two uses for the single product and no worries re disposal of chemicals.
One last thing I thought of; are you on an OMF? - if not you may need rather more bottom ventilation than a relatively narrow (as in width) slot to maintain a dry atmosphere in the hive over winter. Of course, OMFs are easy enough to make, too. And don't forget to check your narrow entrance often over winter as there is a greater risk of it getting blocked by dead bees and other detritus.
Regards, RAB