What sort of units ?
Pre filled umits or separates that need to be filled post install ?
If it is the second then price of the gas needs to be added to cost of units, and as 9kg of R32 can be anywhere up to almost £500 in places, and will only ever go up in price, month on month, you can see why quotes can vary a lot as no one really knows exactly what the price of gas will be next week, let alone next month or next year.
At work we just had a quote for 200kg of R23 and that was £35,000, and that is to re gas just one of our 18 environmental chambers.
The R23 is around £130 per kilo now, this time last year it was about £19