We didn't have a wedding car - just drove to the pay and display car park near the registry office in our own car and walked across. It helped that my wedding dress was a tea dress shape rather than the full shebang.
I also got married in Lincolnshire, despite not being from around there, as we had hired an air b n b I saw on sale to be the weekend venue. It was Louth registry office which was lovely and had a beautiful room.
We didn't have a professional photographer - but we had loads of photos. I asked my brother to arrange the formal shots (he's not a photographer) and he did a couple on a timer/tripod where he joined us. I asked everyone else to share their photos with me and we have loads.
I didn't have a florist. I did spend a couple of hundred pounds on roses (I think they came from Jersey) and wrapped my own into a bouquet, i made button holes and table flowers with these. There were 2 bucket fulls of beautiful flowers (2013 prices). I think you could easily make a bouquet of supermarket roses and not bother beyond that.
How about asking a local restaurant e.g. an Indian restaurant to quote for an afternoon buffet? That would be for a smallish group with your budget.
If you want a party you could go for an afternoon wedding then use the barn for a buffet and dj/band. Could your family/friends help with a buffet spread? Does the barn have a bar? If not how about "bring your own booze" with you providing some table wine/jugs of water and pop?
Then use your budget for some live music (post on a music Facebook group for your area and let them know your budget e.g. £200) and a DJ.
Just to add if your income is ok and you aren't struggling with debt I would up your budget a little with a 0% purchases credit card or a small loan. But perhaps that's a bad attitude!