It depends on what you need to change to get the trunk to match. If it is just the front panel, then buying a used trunk and changing the front panel out is easy and cost effective.
If it is changing out the front, two side panels and a lid and painting or staining the bumpers, you will be better off to sell your trunk to the last barn and then purchase a new one.
For all of the above, I’m assuming that you are talking about a vinyl paneled trunk.
The panels aren’t difficult to change out. Most of the time the guys at the barn do it. If you’re at a big show barn, they have more than likely done a lot of them over the years.
Whomever said that you can’t change out a lid is partially correct. This isn’t something that you can do yourself because the metal needs to be wrapped around the lid and I guess it is difficult to do. You would have to mail the old lid back to the company and have them redo it. By the time you factor in shipping both ways, you’re better off just getting a new lid.
If you know who made the trunk, you can get a quote to replace what you need. Options such as extra letters, piping, extra borders and special logos can really add up. Your local tack store can help you with pricing even if they didn’t order the initial one. All of the trunk manufacturers keep detailed info on each barn’s custom orders.
Also, keep in mind too that shipping a large trunk requires it to be sent via a freight company and that is about $150+ depending on where it is going and what the cost of gas is at the moment and if there are others on that shipment. Medium and small trunks may be sent via UPS etc so they are much cheaper to send.
As far as making your own trunk, I personally wouldn’t do it. You will always be the odd person out with a non-matching trunk and depending on how OCD your trainer is about matching things at shows, you’ll probably be placed at the end of the aisle if your trunk doesn’t match. I’ve also not seen a home-made trunk that lasts the test of time like the Phoenix West/McGuinn’s trunks. I’ve not had experience with Oakcroft but have seen other fly by night vendors whose trunks were not durable. We have Phoenix West trunks 20 plus years still looking great.
Before I get flamed for how shallow the H/J world is, show set ups are important as a marketing tool etc for many of the trainers and they want to present themselves professionally and so the matching trunks will generally be at the front of the barn. This may not be an issue to you at all, but for some they don’t like being at the far end of the barn aisle.