Not exactly a 90 day visa added to the end of the METV but rather another 60 day stay and then a 30 day Extension can be added. Terminology is important because it is what Thai Immigration and Consular officers use

With a Thailand METV you don't need any sort of other document or permission to get into Thailand. Your passport will just be stamped as having entered. The METV gives you a 60 day stay every time you Exit and Reenter Thailand for the 6 month life of the METV - then an Exit and Reentry just before the Expiry date of the METV gives you another 60 days. You can get a 30 day Extension to any one or all of the 60 day stays. Or you a mix and match. When you go out of Thailand to a regional Embassy / Consulate and actually get the Non Imm O Visa 90 day visa the METV is finished and the Non Imm O visa is in use when you reenter Thailand.

BUT BACK TO Travel Costs. You need to check the airlines but air tickets, travel costs, hotel room fees, etc. to any regional country to get a Thailand Visa is much the same when flying out of Bangkok. Air Asia, Thai Lion Air, Bangkok Air and others fly to most all the regional capitals.

Laos Visa on Arrival is 1600-1800 Baht (I forget exactly)

You have to apply for the Non Imm O single entry 90 day Thailand visa at a Thai Embassy/ Consulate. But this Non Imm O can be obtained in Bkk

No you have to buy the Foreign neighbor country Visa on Arrival. Malaysia - Penang has no fee. Penang can be reached by a flight from Bkk via Air Asia. Agents are there that can do it all for you while you make a walking tour of old Georgetown.

To get a 90 day Non Imm O visa in the Thailand region and the subsequent one year Extension of Stay - you can use proof of monthly income from out of Thailand - equivalent to 65,000 Baht a month. Depending on your home country Bangkok Embassy rules - a certificate / letter of income is available for a fee and certain proof of income.

Thailand really does not have a Visa Renewal system - you just start over again

If you want another O-A Visa you have to get it in your home country - same as the first one.

I have read that a Multi Entry O visa (without any justification except being over age 50) had recently been issued in the UK but it is not commonly done and not done at all in the USA... But you are not going to get a Non Imm Multi O in the Thailand region unless married to a Thai or have custody of your Thai children here.

Then you have to get a 90 day Non Imm O visa then apply for the One Year Extension of Stay.

The O Visa single entry can be obtained in Vientiane, Savannakhet , Penang and other places in the region AND at the main immigration office in Bangkok