We are renovating a derelict property and the last kitchen cabinet was fitted today!
Carpenter/kitchen fitter said to avoid wren at all costs. We went to B&Q, Wickes (I think they are benchmarxs), brewers- looked online at ikea and also several local shops. Some came out to give us a free design. Each gave slightly different ideas which was very handy. Look at the work triangle to ensure you aren't walking too far from fridge/sink/cooker etc. look online and think about what style you are going for? Shaker, modern shaker, modern flat, matte, shiny or the MANY other styles and options out there. Handless or handles? Have an idea of things you must have, nice to have and don't need. I knew I wanted more drawers so no bending to back of low cupboards. I also wanted an integrated bin drawer and floor to ceiling cupboards on one side to make use of the space.
If you have an island, where possible, don't have a sink or hob on it. It can be more expensive for electrics/exhaust fans etc, plus I don't like having either things in the sink to be washed up, or things drying on display in the middle of the island. Nor having a dirty hob. If they are on the side walls, they aren't right in the island nor as noticeable IMO.
We ended up going with a local man. No shop, works from home but has access to 100's of cabinets/doors/handles etc. We got various quotes from the mainstream places (no appliances or worktop) ranging from £15-£22,000. The independent guy came in at about £10,000 for solid wood doors and all the internal parts- like drawers, cutlery trays, pull out metal larder things and a fancy, metal full out corner contraption. The door we have- is the exact same one we liked in the most expensive shop too! Our worktops came from a local company. Including a large island and utility it came to £9,000 for quartz. Same size in granite would have been £14,000. They had cheaper options- we just happened to pick a pricier quartz apparently!
Buy appliances yourself from AO/marks electrical etc. Have a competent kitchen fitter/carpenter. Ours has been fabulous, but a friend had one recently walk out as they were too overwhelmed!
Another option we did years ago in a flat was to just have the doors redone- if the basic layout works for you. The previous doors were peeling so we replaced the doors and handles for a fraction of the cost of a whole new kitchen. People assumed we'd had the whole thing re done. It still looked great 10yrs on.