Tanning in a bed is no worse for you than being in the sun.....matter of fact tanning in moderation to build a base tan before being in the sun is far better for you than burning. You absolutely do not want to burn!!!!!
There are lots of different types of tanning equipment and all have different exposure times. My recommendation would to be to look at the piece of equipment you plan to use and go by the lable for exposure times. most beds it is 3-5 mintues per session for the first 2-4 session and work up progressively from there. Most salons will encourage you to go longer...do not do it!!! Those recommendations are for a reason. I have 4 tanning salons and follow these guidelines for new clients and every one of them get tan. We do not allow our customers to tan more than every other day and ask to see their FDA approved eye protection each visit. We preach moderation, and good skin care and eye protection. Not all salons are like this unfortunately

Tanning lotions sold by your salon will help you build more melanin so you will therefore tan quicker plus they have high quality moisurtizer and skin care ingredients to keep your skin healthy and hydrated.
Cost will vary significantly across the nations...even within a town.. I would steer clear of a tan for a month for $XX. And find a high end salon that will sell you the number of session you need to get your desired color.
It takes 8-10 sessions to get a base tan so allow at least 3-4 weeks.
Spray tan is cosmedic and will give you a nice looking glow, most sprays last 5-7 days with optimum results the first 2-3 days. It is a good option if you want to look nice and golden. Spray tans are purely cosmedic and will not stop you from burning in the real sun.
Are tanning beds good for you???? NO
But neither is drinking city water, breathing polluted air, drinking caffeine, eating fats, etc.
I think (only my opinion) that moderate UV exposure in tanning equipment to acheive or maintain a base tan for an event or for day to day life is no worse for you than anything else we do to ourselves. But only you can decide what is right for you. I do not encourage or endorse prolonged repeated exposure for anyone, and I make my living off of these devices.
Also remember no matter how dark a tan you have, you can still burn when exposed to the sun for long periods of time, so ALWAYS use a SPF when planning on being outdoors (even on cloudy days).