Matt,
These are from Warbase.
The goods wagon is £4.50. It could easily be cut down to a milk cart . Or replace the wheels with tyred wheels.
I'm not a big fan of their lorries( not for the obvious reasons,but for the over use of MDF. For parts that would be better in thinner materials)
But I do like they're carts and wagons ,worth the money.
The Sarrisa (painted wagon) has the edge as its from more experienced designers but its nearly twice the price at £7.50. Either route is ,with postage going to come in close to your €15 limit.
Having said that you could knock your own up in plasticard in under an hour,and re use some old tyred wheels.
Mark.