hi! welcome to RU :wave:
something like this should go in the "health" section of the forum, but one of the forum mods will likely move it there for you shortly.
I'm really sorry to hear about your bunny, its an incredibly stressful and difficult time for all of you. I went through something similar, and it was very draining both financially and emotionally.
out of interest, what is his diet like? perhaps something can be changed within it to help lengthen the process between dentals. not saying you are doing anything wrong either, but even with the perfect diet perhaps something can be adjusted to suit the situation.
with something like this, it would possibly point to breeding defects. lops and minis/dwarfs tend to have very rounded and short muzzles, and there just isn't the room for the teeth to grow. it can cause roots to become elongated, teeth to grow into their jaw, or just grow incorrectly. its extremely unfortunate.
I would really recommend getting some x-rays done of his jaw. it would give huge insight to how they are growing and what's going on. if he's unable to have a general anaesthetic, they might be able to get some while he's awake, or just made slightly drowsy.
do you have any medications for him? I know for my bun (Snoopy) he was on almost permanent randititine and another gut stimulant to help keep things moving. along with that, he had a low dose of metacam since his teeth were (more than likely) growing into his jaw. unfortunately he was a very poorly bunny and along with his teeth being not as they should, be suffered from stasis plenty, which didn't aid his cause either. it might be something to discuss with your vet.
unfortunately, some bunnies have to have monthly dentals. many here on RU have bunnies who need dentals every 4-8 weeks or so. its a very tiring process, but many of them live healthy & happy lives.
depending on the x-rays, it may or may not be an idea to have his back teeth removed...its a very big operation I will admit. but, they can survive wonderfully well without their back teeth, you just have to make some adjustments to their diet. I'm sure another RU member can provide some insight into that, as I'm not too knowledgeable there.
fibre is incredibly important to bunnies and helps keep tummy moving, it might be worth offering some fibrefirst sticks from science selective. mine love them, if he is struggling to eat hay, then I would suggest offering a large amount of them to help him.
http://www.petsathome.com/shop/en/pets/fibafirst-rabbit-2kg
fibreplex may also be an idea, but once again I'm not too sure so I'm hoping somebody else can run by and give a yay or nay
https://www.vetuk.co.uk/rabbit-supp...ibreplex-for-rabbits-and-small-rodents-p-1180
along with that, I know for Snoopy having probiotic in his water did amazingly well for him. once I used that, stasis happened a little less. and when he was in stasis, some warm water with the probiotic would sometimes sort him out
http://www.petsathome.com/shop/en/pets/proc-probiotic-100gm
unfortunately, my little Snoopy passed away. however, many many other bunnies have lived to tell the tale of dental issues, and pooped in its face
its not an ending for them unless it really is the kindest or there is nothing that can be done. but, I believe there are plenty of other options still currently left on the table. if he is fit and healthy apart from this, I believe more can be done.
if money is an issue, there may be funding you can apply for, or some vets will do payment plans.
I wish the best to both you and bunny, and another welcome to RU