Why would you want someone else to fence your allotment ? It's not a difficult job technically, just a matter of bashing in some posts and joining up the dots ... my new neighbours don't have a lot of spare time but are fencing as they go, weeding and digging as they go, planting a few beds, and covering the rest they won't get to until the end of the season. That first year seems to be all important for all of us and how we intend to continue or not.
Seeds and plants, replacing pots etc, cost me roughly £100 a year. If I were disciplined enough, and a bit more organised, it could cost me half of that, but we all have our weaknesses, mistakes and desires. A nice new cherry tree would set me back £30. I would love one, but I'll just have to dream. Any sheds and greenhouse are on top at the beginning obviously. I personally think a greenhouse is an essential part of allotment things these days considering the climate. The 12 x 6 greenhouse I built cost me £200 all in, rather than three times the price off the peg flat pack..
In the end, it's a pleasure, a hobby, a healthy activity, a source of quality cheap food, a a community, a muse... whatever one wants it to be. Many of us think nothing of spending a lot of money on a night out, so allotments are enduring value for money.
These thoughts come from one of the most frugal people you would ever meet. I also thought I would not enjoy repetitive digging for very little recompense. I was wrong, on occasion it brightens my day, and the Summers are infinitely longer now. In money specifics, I saw purple sprouting broccoli for sale in a supermarket last week for £7 per kg !! and that wasn't even organic. Enough said