To obtain consistent results, you should color calibrate your output devices and use a print service for which color correction profiles are available. Dry Creek Photo privides ICC profiles for print services, including many Costco locations.
Rather than buying new equipment, I'd suggest going through several recalibration-usage cycles over several months. This way, you can learn:
- How to calibrate and recalibrate your devices.
- What to expect from calibration.
- What the real limits of your equipment are.
- What to look for should you decide to buy new equipment.
The more accurate the calibration, the more involved the process, and the more frequent recalibration, will need to be. However, getting exact shades of colors usually isn't that important if you're intended outputs are primarily digital, where most people viewing your work will not have calibrated monitors.
The main points of calibration are white balance, gamma, and brightness. If you can get these right, you should be able to get satisfactory output from most print services. (Use sRGB, and disable auto-adjustments when ordering.)
A problem you will likely encounter while attempting to calibrate LCD displays is viewing angle changes the "gamma". This is particularly noticeable on large screens where the viewing angle from edge to edge differs drastically. Calibrate the center as well as you can for orthogonal viewing. Then when more critical evaluation is necessary, take a few steps back.