30 quid / day????
When I was in an industry that hired lots of stuff, the going rate, for VERY expensive kit, (and the cheapest) was around 1% of the capital cost per day. Not per hour! Even then, you still easily recoup the outlay on popular items within a year. I have often contemplated buying shares in Jewsons - they know their direct customers aren't price sensitive, as they in turn pass on costs to the ultimate client.
Bear in mind too, that the hire counter probably knows next-to-nothing about router care & feeding (and probably
doesn't care), neither do previous hirers. If you can, take a knowledgeable mate with you when you hire, to check the machine out before you accept it. In particular look for collet wear and any float in the shaft. 90% of the time they've probably been used for kitchen worktops, and in the hands of a novice, that means bearing and collet wear (as they try to take too-deep cuts with gummy or dull cutters).
Yours is one of those tasks where a good-quality router in good nick will make shedloads of difference, as will the quality of the trammel arrangement you contrive -- straightness, parallelism and sag of the crosspiece(s). The better you can do the powered part, the less stock you will waste and the less sanding later to finish.
Bear in mind also that fitting your router to the trammel box, or adapting the trammel box to the router will also come out of your hire cost.
And it would be a good idea to practice on some cheap stock too. I've got
Wealden's six-wing cutter, and have used it a lot for small jobs where it's worked well. So it was a surprise how pernickety it was when I had to do a big slab of oak, which was rather precious to its owner. That said, the method saved the piece, as we could micro-adjust it to eliminate wind with minimum waste - putting it through a planer without a sled would almost certainly have been a disaster.
There are a number of good YouTube tutorials on doing this, too.
Can you make thin wedges? Do you have a good method planned for holding the workpiece down? Your first task will almost certainly be getting one side out of wind, so do you have a flat enough and big enough surface to work on?
Plan carefully and if you _must_ hire, get everything as ready as possible beforehand (e.g. find the mounting hole positions on the router plate via t'internet,
before hiring).
Final thought though: is there any workshop near you who has a wide enough spiral block planer/thicknesser? The finish is remarkable usually, and it might be worth paying the hire fee to them instead!
E.
PS: That six-wing cutter is 38.90 (plus postage). Where did you get 100 quid from - are those gold-plated?
